ISLAM IS A RELIGION CREATED BY PLAGIARISM.
The sycophants of Islam and its followers have long worked hard to tie the three Religions of the Mid East to each other. Islam very cleverly weaves Adam and Abraham and the Old Testament of the Bible into its heresy.
Yes Islam had a lot of time to listen, read and weave all the stories of the older Religions into its new book. Below is a detailed expose of the facts that are undeniable. Mohammed was a plagiarist!
MUHAMMAD THE "BORROWER" FROM OLDER RELIGIONS!
Since Islam began people have charged Muhammad with borrowing stories and religious material from other religions and repeating them as the Quran. Muhammad's contemporaries had heard those stories before and voiced that Muhammad was repeating them. The exposure of Muhammad's borrowing continues to this day. Modern Islamic scholars continue the assertion. These scholars come from Atheist, Jewish, Christian, and even Muslim backgrounds. They've all agreed that Muhammad borrowed religious material. A moderate selection of quotes from about a dozen scholars is presented at the end.
Specifically, scholars assert that primarily Muhammad borrowed from Judaism and Christianity. He also borrowed from Arabic paganism. They add that he injected quite a bit of his own concepts, desires, and philosophy, into the Quran.
On the other hand fundamentalist Muslims claim, as Muhammad claimed, that he received pure revelations from a spirit he identified as the angel "Gabriel". They believe that this spirit, "Gabriel" had previously received these words from God and repeated them to Muhammad. Muhammad then recited them as the Quran. (YEAH RIGHT !! THAT'S AN EASY WAY TO GET AROUND PLAGIARISM!!)
Interestingly, the Quran records this charge of borrowing leveled against Muhammad by his contemporaries:
And they say: "Tales of the ancients, which he has caused to be written: and they are dictated before him morning and evening."
"We know indeed that they say "It is a man that teaches him." The tongue of him they wickedly point to is notable foreign while this is Arabic pure and clear. Those who believe not in the Signs of Allah, Allah will not guide them and theirs will be a grievous Penalty." (Yusef Ali's translation) 
Why did Muhammad's contemporaries say that Muhammad borrowed from other religions or fables? Why do today's scholars make the same exact charge? What is the basis of their accusations and statements? Do they have ground to stand on? Or is it, as some fundamentalist Muslims claim, a conspiracy to defraud Muhammad and Islam?
What is at stake is this: if there is evidence that Muhammad borrowed other religious material the Quran would be invalidated as being pure revelation from God. Wouldn't that make the Quran a deception and Muhammad an impostor?
I'll point out that when Muhammad first encountered this "spirit", the experience drove him to attempt suicide. Oddly enough, it was this same spirit that prevented him from killing himself. See the webpages related to Muhammad’s Suicide Attempts, and Muhammad and the Demons, for information on Muhammad's interaction with spirits.
What follows is the evidence of Muhammad's borrowing. I will "bring forth some proof", as Muslims say, and produce material in the Quran that has been borrowed from other sources.
Let's start with two simple cases: Muhammad borrowing from the Jewish Mishnah concerning 1) Cain and Abel, and 2) Abraham. 
1) The Quran's story is found in Sura 5:27-32. Initially, the O.T. and Quran basically agree on the narrative. In verse 31, the two diverge.
"That is why we laid it down for the Israelites that whoever killed a human being, except as punishment for murder or other villainy in the land, shall be deemed as though he had killed all mankind; and that whoever saved a human life shall be deemed as though he had saved all mankind.".
Initially, there appears to be no connection between verses 31 and 32. Why the life or death of one should be as the salvation or destruction of all mankind in not made clear in the Quran. When we turn to another Jewish record - the Mishnah Sanhedrin, we find the link between the story and what follows:
"We find it said in the case of Cain who murdered his brother, 'The voice of thy brother's bloods crieth' (Gen. 4:10). It is not said here blood in the singular, but bloods in the plural, that is, his own blood and the blood of his seed. Man was created single in order to show that to him who kills a single individual it shall be reckoned that he has slain the whole race, but to him who preserves the life of a single individual it is counted that he hath preserved the whole race." Mishnah Sanhedrin, 4:5
Here in the Quran is a passage from the Mishnah! The Mishnah is a Jewish commentary on the Torah. How did a Rabbi's commentary on the Torah make its way into the Quran? Simple, Muhammad had heard these teachings from the Jews, and repeated them later as he recited "revelation".
Because the word for blood is in the plural in Gen. 4:10, an ingenious Rabbi invented the supposition that all Abel's offspring had been killed with him which signified that any murder or life-saving act had universal implications. Clearly Muhammad had no knowledge of the source of the theory set out in the Mishnah but, in hearing it related, simply set out the Rabbi's suppositions as the eternal decree of God! Now today, some Jewish Rabbi's thoughts are quoted as revelation in the Quran!
This short piece clearly shows, in one way at least, how Muhammad received "revelations". In this case, verbal stories told by the Jews, and Muhammad's memory served him. Here the Quran fails the test of authenticity; it owes much of its substance to other faiths. For some reason Muhammad decided to quote a Jewish story, feeling it has some important meaning, and placed into the Quran. Little did Muhammad know or really understand from what he was really quoting.
NOTE: Dating of the Mishnah Sanhedrin is as follows, from the Encyclopedia Judaica, 1996, Keter Publishing House Jerusalem
"Commitment to writing began about the middle of the 3rd century CE with RAV (Abba Aricha) and Samuel and was completed with the conclusion of the teaching of Ravina in 499 AD."
Likewise the "Introduction to the Babylonian Talmud", Soncino Press edition by Dr. J.H. Hertz states that the Babylonian Talmud
" Claims origins from the Babylonian captivity proclaiming the religious and civil law fixed in 444 BEC by Ezra the Sofer (The Biblical Ezra the Scribe) and finalized in 500 AD."
Both these references state that the writing related to 5:32 predate Muhammad.
2) There is another passage in the Quran that has its origins in the Mishnah. This passage is Sura 21:51-71. The Mishnah passage is found in Rabbah Genesis.
Here is the Quranic story:
We formerly bestowed guidance on Abraham, for We knew him well. He said to his father and to his people: "What are these images to which you are so devoted?" They replied: "They are the gods our fathers worshipped." He said: "Then you are your fathers are in the grossest error." "Is this the truth that you are preaching," they asked, "or is this but a jest?" "Indeed," he answered, "Your Lord is the Lord of the heavens and the earth. It was He that made them: to this I bear witness. By the Lord, I will overthrow your idols as soon as you have turned your backs." He broke them all in pieces, except their supreme god, so that they might return to him. "Who has done this to our deities?" asked some. "He must surely be a wicked man." Others replied: "We have heard a youth called Abraham speak of them." They said: "then bring him here in sight of all the people, that they may act as witnesses." "Abraham," they said, "was it you who did this to our deities?" "No," he replied. "It was their chief who smote them. Ask them, if they can speak." Thereupon they turned their thoughts upon themselves and said to each other: "Surely you are the ones who have done wrong." [Confounded as they were, they said to Abraham:] "You know they cannot speak." He answered: "Would you then worship that, instead of God, which can neither help nor harm you? Shame on you and on your idols! Have you no sense?" They cried: "Burn him and avenge your gods, if you must punish him!" "Fire," We said, "be cool to Abraham and keep him safe."
Here is the quote from the Mishnah Rabbah, Genesis (Noach) (CH 38:11-13) Vol. 1, pp. 310 -311, Soncino Edition, Soncino Press London, Editors Dr H Freedman and Maurice Simon. 
13. AND HARAN DIED IN THE PRESENCE OF HIS FATHER TERAH (XI,28). R Hiyya said: Terah was a manufacturer of idols. He once went away somewhere and left Abraham to sell them in his place. A man came and wished to buy one. 'How old are you?' Abraham asked him 'Fifty years' was the reply 'Woe to such a man!' he exclaimed. 'You are fifty years old and would worship a day old object!' At this he became ashamed and departed.
On another occasion a woman came with a plateful of flour and requested him, 'Take this and offer it to them.' So he took a stick and broke them and put the stick in the hand of the largest. When his father returned he demanded, 'What have you done to them?' 'I cannot concealed it from you' he rejoined. "A woman came with a plateful of fine meal and requested me to offer it to them. One claimed 'I must eat first' while another claimed 'I must eat first'. Thereupon the largest arose, took the stick, and broke them." 'Why do you make sport of me' he cried out; 'have they any knowledge!' 'Should not your ears listen to what your mouth is saying' he retorted. Thereupon he seized him and delivered him to Nimrod.
'Let us worship fire' he (Nimrod) proposed. 'Let us rather worship water', which extinguishes the fire' replied he. 'Then let us worship water!' ' Let us rather worship the clouds which bear the water.' 'The let us worship the clouds!' 'Let us rather worship the winds which disperse the clouds' 'Let us worship the wind!' 'Let us worship human beings, who withstand the wind' 'You are just bandying words' he exclaimed; 'We will worship naught but fire. Behold, I will cast you into it, and let the God whom you adore come and save you from it.
Now Haran was standing there undecided. If Abram is victorious, (he thought), I will say that I am of Abram's belief, while if Nimrod is victorious I will say that I am on Nimrod's side. When Abram descended into the fiery furnace and was saved, he (Nimrod) asked him, 'of whose belief are you?' 'Of Abram's' he replied. Thereupon he seized and cast him into the fire; his inwards were scorched and he died in his father's presence. Hence it is written, AND HARAN DIED IN THE PRESENCE OF ('AL PENE) HIS FATHER TERAH.
It is clear that Muhammad borrowed from Jewish legend. He added a few details, just as all story-tellers do, to embellish the story according to his needs or fancies. Also notice that although the Quran does not name Nimrod as the king, as the Mishnah does, the Islamic historian Tabari refers to this incident and names him. On page 59 of volume 4,: "god moved Nebuchadnezzarb. Nabuzeradan b. Sennacherib b. Darius b. Nimrod (the one who disputed with Abraham concerning his Lord)...
1) The Rabbis translate ''Al Pene' 'Because of' : He died because his father manufactured idols.
THE QURAN AND THE NEW TESTAMENT APOCRYPHA
There are many quotes in the Quran that come from New Testament Apocrypha. I will not list all of the quotes because many of them are repetitions. Also, there are many references in the Quran to Christian themes, but they are redundant. Taken as a whole, there is a paucity of detail in the Quran regarding Christian teachings. As Watt said earlier, Muhammad and the Quran lack an alarming amount of actual detail with respect to Christianity.
That being said, I will list a selection of the borrowed Christian themes found in the Quran to demonstrate that Muhammad obtained some of his "Quran" from Christians or those that had knowledge of general Christian themes as documented and known by the church at that time (A.D. 610 - 632).
A From the Quran - Sura 19 - "Mary", verses 28 - 33
Carrying the child, she came to her people, who said to her: 'Mary, this is indeed a strange thing! Sister of Aaron, your father was never a whore-monger, nor was your mother a harlot.'
She made a sign to them, pointing to the child. But they replied: 'How can we speak with a babe in the cradle?'
Whereupon he spoke and said: 'I am the servant of God. He has given me the Book and ordained me a prophet. His blessing is upon me wherever I go, and He has exhorted me to be steadfast in prayer and to give alms as long as I shall live. He has exhorted me to honor my mother and has purged me of vanity and wickedness. Blessed was I on the day I was born, and blessed I shall be on the day of my death and on the day I shall be raised to life.' (Dawood's translation).
The source of this story is "The Arabic Infancy Gospel". There exists a whole collection of stories and fables classified as "Infancy Gospels". Later ones were based upon earlier ones. The Arabic Infancy Gospel is based upon earlier Infancy Gospels were created from the second century onward. Here is the quote from The Arabic Infancy Gospel:
"We find what follows in the book of Joseph the high priest, who lived in the time of Christ. Some say that he is Caiaphas. He has said that Jesus spoke, and, indeed, when He was lying in His cradle said to Mary His mother: I am Jesus, the Son of God, the Logos, whom thou hast brought forth, as the Angel Gabriel announced to thee; and my Father has sent me for the salvation of the world."
One scholar - J. K. Elliot writes regarding the dating of the Arabic Infancy Gospel, in "The Apocryphal New Testament", page 100:
"This is another collection of material that has made use of the Protevangelium of James (PJ) and Infancy Thomas. Chapters 1 - 10 are based up PJ, and 36-55 shows many similarities with Thomas... In between (i.e. chapters 11-35) the author has drawn on a large collection of fantasies, the origin of which is likely to be Egyptian.
"...the Arabic is likely to go back to a Syrian archetype, which could be of he fifth - sixth century." 
M. R. James in "The Apocryphal New Testament", pub. by Oxford, writes on page 38 regarding "The Protevangelium of James",
"Origen mentions the Book of James as stating that the brethren of the Lord" were sons of Joseph by a former wife. This is the first mention of it and shows us that the book is as old as the second century." 
Regarding the composition date of the Infancy Gospel of Thomas, Helmut Koester writes in "Ancient Christian Gospels" on page 311:
"That this writing existed in some form in the 2nd century is not certain but also not improbable. 
And Elliot writes regarding the "Infancy Gospel of Thomas",
"Wright's Syriac text is based on a fifth century manuscript that is close to Greek A.
Hennecke writes in "New Testament Apocrypha", pub. by Lutterworth, page 369:
"The basis of all the vast later literature constituting the apocryphal infancy gospels is the so called Protevangelium of James, probably of the 2nd century, particularly for the birth, childhood and motherhood of Mary, and the Gospel of Thomas, not much later in its original form, for the miracles of the child Jesus." 
Fables through time have changed, and Muhammad repeated one of the variations of Jesus speaking in the cradle. Thus the fable of Jesus speaking in the cradle predates Islam.
The text of the Arabic Infancy Gospel can be found at
B From Sura 19 - Mary: verses 22 - 26
Thereupon she conceived him, and retired to a far-off place. And when she felt the throes of childbirth she lay down by the trunk of a palm-tree, crying: 'Oh, would that I had died and passed into oblivion!'
But a voice from below cried out to her: 'Do not despair. Your Lord has provided a brook that runs at your feet, and if you shake the trunk of this palm-tree it will drop fresh ripe dates in your lap. Therefore eat and drink and rejoice; and should you meet any mortal say to him: "I have vowed a fast to the Merciful and will not speak with any man today."'
From Sura 23 - The Believers, verse 50:
We made the son of Mary and his mother a sign to mankind, and gave them a shelter on a peaceful hillside watered by a fresh spring.
These two verses relate to the birth of Jesus. The parallel is found in "The Gospel of Pseudo Matthew", as follows:
Now on the third day of their journey, as they went on, it happened that blessed Mary was wearied by the too great heat of the sun in the desert, and seeing a palm tree, she said to Joseph: "I should like to rest a little in the shade of this tree." And Joseph led her quickly to the palm and let her dismount from her animal . And when blessed Mary had sat down she looked up at the top of the palm tree and saw that it was full of fruits, and said to Joseph: "I wish someone could fetch some of these fruits of the palm tree." And Joseph said to her: "I wonder that you say this; for you see how high this palm tree is, and (I wonder ) that you even think about eating of the fruits of the palm. I think rather of the lack of water, which already fails us n the skins, and we have nothing with which we can re-fresh ourselves and the animals."
Then the child Jesus, who was sitting with a happy countenance in his mother's lap, said to the palm: "Bend down your branches, O Tree and refresh my mother with your fruit." And immediately at this command the palm bent its head down to the feet of blessed Mary, and they gathered from it fruits with which they all refreshed themselves.....Then Jesus said to it: "Raise yourself, O palm .....and let the waters flow so that we may quench our thirst from it." And immediately it raised itself, and there began to gush out by its root a fountain of water very clear, fresh and completely bright. 
The quote above is from "New Testament Apocrypha", by E. Hennecke, edited by Schneemelcher, published by WJKP, page 463.
The Gospel of Pseudo Matthew was based upon earlier Apocryphyal Infancy Gospels, namely, the "Protoevangelium of James" and "The Infancy Gospel of Thomas". These two Infancy Gospels form the basis for many other "Infancy Gospels".
M. R. James in "The Apocryphal New Testament", pub. by Oxford, writes regarding the Pseudo Matthew, on page 70
"The two main sources are the Protevangelium (of James) and the (Infancy) Gospel of Thomas, but some few episodes are not found in either.
Jacques Hervieux writes in "The New Testament Apocrypha", published by Hawthorn Books, page 18:
"About the sixth century there appeared in Latin a certain book on the birth of the Blessed Mary and of the Savior's infancy. An introductory letter presented this new work as a "supplement" to the Gospel of St. Matthew, translated personally by St. Jerome the great fourth century exegete."
Elliot writes in "The Apocryphal New Testament", page 86:
"In the Gelasian Decree, no. 8 refers to Evangelia nomine Jacobi mnoris, which Amann (p. 104) identifies with PJ, but de Strycker (La Forme la plus ancienne..., p. 43 n. 1) raises the possibility that this could b ePseudo-Matthew. If so, then Pseudo-Mathew must have been composed before the compilation of the Decree, and this would give it a date prior to the sixth century.
C From the Quran - Sura 3 - "The Imrans:, verses 37 - 37
Remember the words of Imran's wife. 'Lord,' she said, 'I dedicate to Your service that which is in my womb. Accept if from me. You alone hear all and know all.'
And when she was delivered of the child, she said: 'Lord, I have given birth to a daughter' - God well knew of what she was delivered: the male is not like the female - 'and have called her Mary. Protect her and all her descendants from Satan, the Accursed One.'
Her Lord graciously accepted her. He made her grow a goodly child and entrusted her to the care of Zacharias.
Whenever Zacharias visited her in the Shrine he found that she had food with her. 'Mary,' he said, 'where is this food from?'
'It is from God,' she answered. 'God gives without stint to whom He will.'
Here is the story from "The Protevangelium of James".
And behold an angel of the Lord came to her and said: "Anna, Anna, the Lord has heard your prayer. You shall conceive and bear, and your offspring shall be spoken of in the whole world." And Anna said: "As the Lord my God lives, if I bear a child, whether male or female, I will bring it as a gift to the Lord my God, and it shall serve him all the days of its life.".....
.....And her six months were fulfilled, as the angel had said: in the seventh month Anna brought forth. And she said to the midwife: "What have I brought froth?" and the midwife said: "A female." And Anna said: "My soul is magnified this day." And she laid it down. And when the days were fulfilled, Anna purified herself from her childbed and gave suck to the child, and called her name Mary.....
.....When she (Mary) was two years old, Joachim said to Anna: "Let us bring her up to the Temple of the Lord that we may fulfill the promise which we made, lest the Lord send some evil upon us and our gift become unacceptable." And Anna replied let us wait until the third year that the child may not long after her father and mother. And Joachim said: "Very well."
And when the child was three years old, Joachim said: "Let us ......in order that the child may not turn back and her heart be enticed away from the Temple of the Lord." And he did so until they went up to the Temple of the Lord. And the priest, (Zacharias) took her and kissed her and blessed her, saying: "The Lord has magnified your name among all generations; because of you the Lord at the end of the days will manifest his redemption to the children of Israel.
.....And Mary was in the Temple nurtured like a dove and received food from the hand of an angel.
As was previously detailed, the PJ was composed in the 2nd century, well before Muhammad was born. As a story, it circulated throughout the Mideast, and was used as material for other story makers. Muhammad heard versions of this story and repeated them as the Quran.
D From Sura 3 - The Imrans, verse 44
This is an account of a divine secret. We reveal it to you. You were not present when they cast lots to see which of them should have charge of Mary; nor were you present when they argued about her.
From "The History of Joseph the Carpenter", by From "The Apocryphal New Testament, by Elliot, 114:
Mary was being brought up in the Temple till she was twelve years old. The priests decided to give her to a husband. The lot fell on Joseph.
A similar story is found in another Infancy Gospel, the "The Nativity of Mary"
Now there was among the rest Joseph, of the house and family of David, a man of great age: and when all brought their rods, according to the order, he alone withheld his. Wherefore, when nothing in conformity with the divine voice appeared, the high priest thought it necessary to consult God a second time; and He answered, that of those who had been designated, he alone to whom the virgin ought to be espoused had not brought his rod. Joseph, therefore, was found out. For when he had brought his rod, and the dove came from heaven; and settled upon the top of it, it clearly appeared to all that he was the man to whom the virgin should be espoused.
The text of "The Nativity of Mary" can be found at
The text of "The History of Joseph the Carpenter" can be found at
E From Sura 3 - The Imrans, verse 49: (also refer to 5:110, 111)
.....He will say: "I bring you a sign from your Lord. From clay I will make for you the likeness of a bird. I shall breathe into it and, by God's leave, it shall become a living bird.....
Here, from "The Infancy Gospel of Thomas" is the source for the Quranic quote.
"The child Jesus, when 5 years of age, was playing on the road by a dirty stream of running water; and having brought it all together into ditches, immediately made it pure and clean; by saying a single word. Then having moistened some earth, he made of it twelve sparrows. And it was the Sabbath day when he did these things. There were many other children playing with him. Now a Jew, seeing what Jesus did, that he was playing on the Sabbath day, went his way to (Jesus') father Joseph. He said, "Behold, your son is at the stream of dirty water, and having taken up some mud, has made of it twelve sparrows, thus desecrating the Sabbath. On this Joseph went to the spot, and cried out, "Why did you do these things on the Sabbath day which it is not lawful to do?" Jesus then clapped his hands at the sparrows and cried aloud to them, "Go off!". So they, clucking, flew away. The Jews seeing it were astonished, and went and told their rulers what they had seen Jesus do."
I've presented Quranic quotes from both Jewish and Christian sources. As was already stated, the Mishnah was composed before Muhammad's time I've also quoted from several New Testament Apocrypha works that are dated well before the creation of Islam.
St. Clair Tisdall summed it up best when he wrote: in "The Original Sources Of The Quran", published by Society For The Promotion Of Christian Knowledge, London pages 210 - 211: 1905:
"From the careful examination of the whole subject dealt with in this chapter (i.e., The Influence Of Christianity & Christian Apocryphal Books) we therefore conclude that the influence of true and genuine Christian teaching upon the Quran and upon Islam in general has been very slight indeed, while on the other hand apocryphal traditions and in certain respects heretical doctrines have a claim to be considered as forming one of the original sources of Muhammadan faith. " 
A WORD ABOUT THE NT APOCRYPHA "INFANCY GOSPELS"
Elliot writes in "The Apocryphal Jesus", page 1:
"These second - third - century inventions may be judged as crudely sensational, magical, or superstitious. Little of this literature maintains the restrained spirituality of the earlier writings that eventually formed the New Testament. Nor do these 'popular' books match the highly intellectual theology of the church father's treatises that are contemporaneous with them."
M.R. James in "The Apocrypha New Testament", writes in his preface, pages xi - xii:
"People may still be heard to say, "After all, these Apocryphal Gospels and Acts, as you call them, are just as interesting as the old ones. It was only by accident or caprice that they were not put into the New Testament." The best answer to such loose talk has always been, and is now, to produce the writings and let them tell their own story. It will very quickly be seen that there is no question of any one's having excluded them from the New Testament: they have done that for themselves.
.....But the authors do not speak with the voices of Paul or of John, or with the quiet simplicity of the three first Gospels. It is not unfair to say that when they attempt the former tone, they are theatrical, and when they essay the latter, they are jejune."
Oscar Cullmann writes in "New Testament Apocrypha", pages 416, 417:
"In the further development of the birth and infancy stories in later days the narrative interests become predominant, although theological interests are still present. The tendency to draw upon extraneous legends, already discernible in the infancy narratives of Matthew and Luke, is greatly increased. The further we move in time from the beginnings, the more unrestrained becomes the application to Jesus of what is recounted about the birth and infancy of sons of gods and children of supernatural origin.... The formation of the canon, which took place about the middle of the 2nd century, was able to check only to a slight degree the legendary accretions which grew up around the childhood of Jesus, ..."
INFORMATION FROM ISLAMIC SOURCES
I've presented half a dozen cases or so detailing the material Muhammad borrowed. There is more, but for time and space, I have not presented a more exhaustive account.
There is a very important point that needs to be established: Muhammad's contact with Christian and Jews or with people who were somewhat knowledgeable about those religions. We have to actually examine the source material. The sources I will use are the Quran, Hadith, and Sirat (biographical material). I will use Bukhari's and Abu Dawud's Hadith, and the Sira of Ibn Ishaq (Sirat Rasulallah), and of Ibn Sa'd (Kitab al-Tabaqat al-Kabir).
Starting with the Quran itself, we will see that there were people who had Jewish and Christian Scriptures with them, and that Muhammad testified to their integrity. [Quotes are from N. J. Dawood's translation of the Quran]. 
PROOF FROM THE QURAN THAT THERE WERE JEWISH AND CHRISTIAN SCRIPTURES IN EXISTENCE AND IN THE HIJAZ DURING MUHAMMAD'S TIME.
In the Quran, 3:48-50, the Scriptures are shown to be existing at Christ's birth:
"He (God) will instruct him (Jesus) in the Scriptures and in wisdom, in the Torah and in the Gospel, and send him forth as an apostle to the Israelites. He will say: "I bring you a sign from your Lord. From clay I will make for you the likeness of a bird. I shall breathe into it and, by God's leave, it shall become a living bird. By God's leave I shall heal the blind man and the leper, and raise the dead to life. I shall tell you what to eat and what to store up in your houses. Surely that will be a sign for you, if you are true believers. I come to confirm the Torah which preceded me and to make lawful to you some of the things you were forbidden."
We see from this verse that not only was God going to teach Jesus the Torah that existed in Jesus' time, but that Jesus came to "confirm the Torah", and to "make lawful to you some of the things they were forbidden".
Quran, 35:31: "What we have revealed to you in the book is the truth confirming previous scriptures...."
Quran 10:37: "This Koran could not have been devised by any but God. It confirms what was revealed before it and fully explains the Scriptures..."
Likewise these verses show that the Quran testifies to the integrity of the Jewish and Christian scriptures that were in existence during Muhammad's time.
In the words of Dr. Campbell in "The Quran and the Bible in the Light of History and Science", page 38:
"With the other verses discussed above from this section they show that Muhammad acknowledged the existence of a valid Torah and Gospel "under his eyes" 
From the Quran, 7:156, 157: "I will show mercy to those that keep from evil and give alms, and to those that in our signs believe; to those that shall follow the Apostle - the Unlettered Prophet - whom they shall find described in the Torah and the Gospel."
3:78, 79: "And there are some among them who twist their tongues when quoting the Scriptures, so that you may think that what they say is from Scriptures, whereas it is not from the Scriptures. They say: "This is from God," whereas it is not from God. Thus they knowingly ascribe a falsehood to God.
No mortal to whom God has given the Scriptures and whom He has endowed with judgment and prophethood would say to men: "Worship me instead of God." But rather: "Be devoted servants of God, for you have studied and taught the Scriptures.""
3:93, 94: "All food was lawful to the Israelites except what Israel forbade himself before the Torah was revealed. Say: "Bring the Torah and read it, if what you say is true.""
These Quranic verses substantiate that the Jews and Christians had religious texts, i.e., what was believed to be the Torah and the Gospel with them before Muhammad. In the Quran, Muhammad said to the Jews to read the Torah. Clearly, they would have to have the Torah with them in order to read it.
Were the Torah or Gospel in Arabic? They were, but, it really didn’t matter. Since the Jews and Christians knew some of their related teachings they could relate and teach their stories to Muhammad, verbally, in Arabic, in order for him to understand them.
There are many of other Quranic verses I could quote from. Campbell's book lists quite a number of them, but the few I've quoted are enough to show that the Quran proves that there were the Torah and Gospel with the "People of the Book", and that these people were in communication with Muhammad.
PROOF FROM THE HADITH THAT THERE WERE JEWISH AND CHRISTIAN SCRIPTURES IN EXISTENCE AND IN THE HIJAZ DURING MUHAMMAD'S TIME.
In some cases I quote Hadith partially. Several are very long and much of their material has no bearing upon the topic.
Bukhari's quotes are from Khan's translation. 
Dawud's quotes are from Hasan's translation. 
From Bukhari: 9.460:
Narrated Abu Huraira: The people of the Book used to read the Torah in Hebrew and then explain it in Arabic to the Muslims. Allah's Apostle said (to the Muslims). "Do not believe the people of the Book, nor disbelieve them, but say, 'We believe in Allah and whatever is revealed to us, and whatever is revealed to you.' "
Note how this Hadith supports in full the assertions of the Islamic scholars. The People of the Book, i.e., the Christians and / or the Jews, used to read their writings in Hebrew and teach it to the Muslims. This is exactly how Muhammad learned the material he borrowed from the People of the Book. Also note that this Hadith is repeated in 6.12
From Bukhari: 1. 3:
......Khadija then accompanied him to her cousin Waraqa bin Naufal bin Asad bin 'Abdul 'Uzza, who, during the Pre Islamic Period became a Christian and used to write the writing with Hebrew letters. He would write from the Gospel in Hebrew as much as Allah wished him to write......
From Bukhari: 4.605:
Narrated 'Aisha: The Prophet returned to Khadija while his heart was beating rapidly. She took him to Waraqa bin Naufal who was a Christian convert and used to read the Gospels in Arabic Waraqa asked (the Prophet),...
From Bukhari: 6.478:
Narrated Aisha: (the wife of the Prophet) The commencement (of the Divine Inspiration) to Allah's Apostle was in the form of true dreams in his sleep, for he never had a dream but it turned out to be true and clear as the bright daylight......Khadija then took him to Waraqa bin Naufil, the son of Khadija's paternal uncle. Waraqa had been converted to Christianity in the Pre-Islamic Period and used to write Arabic and write of the Gospel in Arabic as much as Allah wished him to write.
From Bukhari: 9.111:
Narrated 'Aisha: .....Khadija then accompanied him to (her cousin) Waraqa bin Naufal bin Asad bin 'Abdul 'Uzza bin Qusai. Waraqa was the son of her paternal uncle, i.e., her father's brother, who during the Pre-Islamic Period became a Christian and used to write the Arabic writing and used to write of the Gospels in Arabic as much as Allah wished him to write.
.......But after a few days Waraqa died and the Divine Inspiration was also paused for a while and the Prophet became so sad as we have heard that he intended several times to throw himself from the tops of high mountains and every time he went up the top of a mountain in order to throw himself down, .......
From the above we learn about Waraqa that he read the Gospels and wrote them in Hebrew and Arabic. So, even there we have Christian material in Arabic. (Note here that in addition to attempted to kill himself after his experience with the spirit "Gabriel", Muhammad attempted suicide after the spirit stopped visiting him.)
From Bukhari: 3.335:
Narrated Ata bin Yasar: I met Abdullah bin 'Amr bin Al-'As and asked him, "Tell me about the description of Allah's Apostle which is mentioned in Torah (i.e. Old Testament.") He replied, 'Yes. By Allah, he is described in Torah with some of the qualities attributed to him in the Quran as follows:
"O Prophet ! We have sent you as a witness (for Allah's True religion) And a
giver of glad tidings (to the faithful believers), And a warner (to the
unbelievers) And guardian of the illiterates. You are My slave and My messenger
(i.e. Apostle). I have named you "Al-Mutawakkil" (who depends upon Allah). You
are neither discourteous, harsh Nor a noisemaker in the markets And you do not
do evil to those Who do evil to you, but you deal With them with forgiveness and
kindness. Allah will not let him (the Prophet) Die till he makes straight the
crooked people by making them say: "None has the right to be worshipped but
Allah," With which will be opened blind eyes And deaf ears and enveloped
[Note that the quote mirrors Isaiah. Muhammad considered Isaiah, or actually the Jewish Canon, the "Torah".
From Bukhari: 4.829:
Narrated 'Abdullah bin 'Umar: The Jews came to Allah's Apostle and told him that a man and a woman from amongst them had committed illegal sexual intercourse. Allah's Apostle said to them, "What do you find in the Torah (old Testament) about the legal punishment of Ar-Rajm (stoning)?" They replied, (But) we announce their crime and lash them." Abdullah bin Salam said, "You are telling a lie; Torah contains the order of Rajm." They brought and opened the Torah and one of them solaced his hand on the Verse of Rajm and read the verses preceding and following it. Abdullah bin Salam said to him, "Lift your hand." When he lifted his hand, the Verse of Rajm was written there. They said, "Muhammad has told the truth; the Torah has the Verse of Rajm. The Prophet then gave the order that both of them should be stoned to death.....
From Bukhari: 9. 77:
Narrated Abu Huraira: While we were in the mosque, Allah's Apostle came out to us and said, "Let us proceed to the Jews." So we went along with him till we reached Bait-al-Midras (a place where the Torah used to be recited and all the Jews of the town used to gather). The Prophet stood up and addressed them, "O Assembly of Jews! Embrace Islam and you will be safe!".....
Notice the threat Muhammad spoke against the Jews? "Embrace Islam and you will be safe"!
FROM THE SUNAN OF ABU DAWUD
Book 3, Number 1041: Narrated Abu Hurayrah:
.......Ka'b read the Torah and said: The Apostle of Allah has spoken the truth. Abu Hurayrah said: I met Abdullah ibn Salam and told him of my meeting with Ka'b.
Abu Dawud: Book 27, Number 3752: Narrated Salman al-Farsi:
I read in the Torah that the blessing of food consists in ablution before it. So I mentioned it to the Prophet. He said: The blessing of food consists in ablution before it and ablution after it.
Abu Dawud Book 38, Number 4434: Narrated Abdullah Ibn Umar:
A group of Jews came and invited the Apostle of Allah to Quff. So he visited them in their school.
They said: Abul Qasim, one of our men has committed fornication with a woman; so pronounce judgment upon them. They placed a cushion for the Apostle of Allah who sat on it and said: Bring the Torah. It was then brought. He then withdrew the cushion from beneath him and placed the Torah on it saying: I believed in thee and in Him Who revealed thee. ............
PROOF FROM THE SIRAT THAT CHRISTIAN AND JEWISH RELIGIOUS WRITINGS EXISTED IN THE HIJAZ DURING MUHAMMAD'S TIME
CHRISTIAN AND JEWISH PRESENCE IN MECCA
I will primarily quote from "The Life of Muhammad", , which is a translation of Ibn Ishaq's "Sirat Rasulallah". Note that this is considered the most authentic biography extent today. Additionally I will quote from Ibn Sa'd's "Kitab al-Tabaqat al-Kabir", .
From pages 14 - 18 the story is told how Christianity began in Najran. Najran is about 350 miles south east of Mecca. The story relates how a Christian preached in Najran, healed the sick, and performed miracles. The whole city converted to Christianity.......
"The people of Najran accepted the religion of Abdullah al Thamir according to the Gospel and the law which Isa b. Maryam brought."
Later on, the story goes, some 20,000 Najran Christians were killed by a king who wanted them to become Jews.
The relevant point here is that there was a Christian city in the Saudi peninsula south of Mecca. Further south was a land ruled by a Jewish king. Certainly there would be cultural exchanges between the cities since Mecca was a center of commerce and religions, and many people traveled to and from there. Hence, there was some knowledge of Christianity and Judaism in Mecca before and during Muhammad's time.
On page 69, the story is told of how Muhammad was conceived. The point of interest is that a women who was earlier interested in Muhammad's father had lost interest in him.....the comment:
"She had heard from her brother Waraqa b. Naufal, who had been a Christian and studied the scriptures, that a prophet would arise among this people."
Here was an Arab a woman, whose brother was a Christian - Waraqa Naufal (the same one mentioned in the Hadith), who had studied the "scriptures", and wrote them in Hebrew and Arabic.
Additionally, from Ibn Sa'd's "Kitab al-Tabaqat al-Kabir", page 104, we read about this women:
"..... (Muhammad's father) passed by a woman of the Kath'am (tribe) whose name was Fatimah Bint Murr and who was the prettiest of all women, in the full bloom of her youth and the most pious and had studied the scriptures;..."
We have a distinct Christian presence in Mecca, and people had "studied the scriptures". These "scriptures" could have been actual Gospels, or apocrypha Gospels.
We read about a Jew living in Mecca in Ibn Sa'd, volume 1, page 186:
"A Jew dwelt at Makkah and sold commodities..."
Note that this keeps in line with what we have already seen about the Jews, they were merchants and business people.
From Ibn Ishaq, page 79, - 81 we read that when Muhammad was a boy, he traveled with his uncle Abu Talib to Syria as part of a caravan
"..... When the caravan reached Busra in Syria, there was a monk there in his cell by the name of Bahira, who was well versed in the knowledge of Christians....There he (Bahira) gained his knowledge from a book that was in the cell, so they allege, handed on from generation to generation.... When Bahira saw him (Muhammad) he stared at him closely, looking at his body and finding traces of his description (in the Christian books)."
From the above we see two things:
1) Muhammad conversed with a Christian who had Christian books with him. Of course he could have learned Christian teachings, true or myth, from Bahira.
2) These books though not in the Hijaz, existed, and the people of the caravans had opportunity to learn of Christianity from the Christians in Syria. They too would have disseminated their knowledge back in Mecca.
Corroborating information on this event is found in Ibn Sa'd, pages 132 - 134, and pages 174 - 177. One detail brought out on page 174 is:
"They halted at Busra, a city of Syria, where there was a monk called Bahira in a covenant, where Christian scholars resided; they had inherited a book which they studied."
Another journey Muhammad took to Syria is described in Ibn Sa'd, pages 145 - 147, and 177 - 179. . Here is an excerpt of a monk's dialog with one of the slaves - Maysarah who accompanied Muhammad on his business journey:
"There the people (of Muhammad's caravan) took rest under the shadow of a tree. Thereupon the monk Nastur said: None except a Prophet has ever taken rest under this tree. .... The man (a person doing business with Muhammad) said, "The word is yours, and turning to Maysarah he said: By Allah! He is a Prophet whose attributes, our scholars have noted in our scriptures."
On page 82, 83, we read about Muhammad's marriage to Khadija. ........
"Khadija had told Waraqa Naufal who was her cousin and a Christian who had studied the scriptures and was a scholar ......"
Here is Waraqa again. Note now he is described as a Christian scholar. He was also Muhammad's wife's cousin. Surely she had conversed with him about Christianity. She in turn would have mentioned these teachings to Muhammad, since Muhammad was interested in religion to the point that he frequently went off in the desert alone to pray and ponder.
On page 84 we read that before Muhammad's self proclamation of prophethood the Kaba needed to be rebuilt and....
"It happened that in Mecca there was a Copt who was a carpenter...."
Again even before Muhammad's rise to power, there was a Christian presence in Mecca.
On page 86, we read that there was actually a biblical quote in the Kaba....
"Layth Abu Sulaym alleged that they found a stone in the Kaba forty years before the prophet's mission, if what they say is true, containing the inscription "He that soweth good shall reap joy; he that soweth evil shall reap sorrow; can you do evil and be rewarded with good? Nay, as grapes cannot be gathered from thorns"
Here we even have a record of a Gospel quote inscribed on a stone!
JEWISH PRESENCE IN MEDINA
On page 93, we read about a dialog between some Jews and some Arabs from Medina disputing...........
"We (the Arabs) were polytheists worshipping idols, while they were people of the scriptures with knowledge which we did not possess."
On pages 95 -97 we read about how Salman the Persian became a Christian.
"So I started out for the farm and when I passed by a Christian (in Persia) church I heard the voices of the men praying."
"I sent to the Christians and asked them if they would tell me when a caravan of Christian merchants came from Syria."
"I stayed with him, (a devout Christian man)"
From the above, we see that there was a Jewish and Christian presence in Mecca, and a Jewish presence in Median, and that Salman the Persian was well acquainted with some Christian teachings, which may or not have been true.
Salman could have taught Muhammad about Christianity. As Muhammad received "revelations", he could have instructed his followers to include verses revealed in Medina to be included with Suras revealed in Mecca.
Back to Waraqa.
On page 99 we read that Waraqa "attached himself to Christianity and studied its scriptures until he had thoroughly mastered them."
And on page 107 we read, "While he (Muhammad), was doing it (circumambulation of the Kaba), Waraqa met him and said, "O son of my brother, tell me what thou hast seen and heard."
So not only was Waraqa a Christian in Mecca, he was noted by Islamic writings as a Christian scholar, who had mastered the Scriptures. And, Waraqa lived near Khadija - Muhammad's wife, and Waraqa even met with Muhammad. So even hear, Muhammad meets with a Christian. Certainly Waraqa could have taught Muhammad his understanding of Christian doctrine, however imperfect it was.
The Gospel according to John.....
There is a very interesting passage on pages 103 - 104 of the Sirat. It deals with the Gospel of John. I will quote it in full because of its bearing.
" Among the things which have reached me about what Jesus the Son of Mary states in the Gospel which he received from God for the followers of the Gospel, in applying a term to describe the apostle of God, is the following. It is extracted from what John the Apostle set down for them when he wrote the Gospel for them from the Testament of Jesus Son of Mary:
"He that hateth me hath hated the Lord. And if I had not done in their presence works which none other before me did, they had not had sin: but from now they are puffed up with pride and think that they will overcome me and also the Lord. But the word that is in the law must be fulfilled, "They hated me without a cause" (i.e., without reason). But when the Comforter has come whom God will send to you from the Lord's presence, and the spirit of truth which will have gone froth from the Lord's presence he (shall bear) witness of me and ye also, because ye have been with me from the beginning. I have spoken to you about this that ye should not be in doubt. (1)
The Munahhemana (God bless and preserve him!) in Syriac is Muhammad; in Greek he is the paraclete."
END OF QUOTE
Guillaume's note (1) for this passage out of the Sirat says:
"The passage quoted is John 15.23 ff. It is interesting to note that the citation comes from the Palestinian Syriac Lectionary and not from the ordinary Bible of the Syriac-speaking Churches. The text is corrupt in one or two places; e.g. the phrase "puffed up with pride and think that they will overcome me". Batiru is an obvious corruption of nazaru, which agrees with the Syriac and underlying Greek. Wazannu seems to be another attempt to make sense of the passage. The next word I am unable to explain. The most interesting word is that rendered "Comforter" which we find in the Palestinian Lectionary, but all other Syriac versions render "paraclete", following the Greek. This word was well established in the Hebrew - and Aramaic - speaking world. The menahhemana in Syriac means the life giver and especially one who raises from the dead. Obviously such a meaning is out of place here and what is meant is one who consoles and comforts people for the loss of one dear to them. This is the meaning in the Talmud and Targum. It ought to be pointed out that by the omission of the words "that is written" before "in the law" quite another meaning is given to the prophecy. The natural rendering would be "the word that concerns the Namus must be fulfilled". To Muslims the Namus was the angel Gabriel. Furthermore, the last words are translated as the ordinary Arab reader would understand tashukku; but in Syrian Arabic it could bear the meaning of the gospel text "stumble". See further my article in Al-Andalus, xv, faxc. 2 (1950) 289-96."
END OF QUOTE OF GUILLAUME'S NOTE
Here is a link for light on Islam's error about the Comforter:
It is obvious to the informed reader, as Guillaume points out, that there was error in the Sirat quote. It again illustrates how Muhammad, and other Muslims learned from word of mouth, and re-quoted if from an imperfect memory. Guillaume notes how the quote in Ibn Ishaq incorrectly defines words in the passage.
Note also how Ibn Ishaq refers to "what John the Apostle sent down for them when he wrote the Gospel for them from the Testament of Jesus Son of Mary"
Obviously, Ibn Ishaq recognized John's Gospel as authentic. He thinks he quotes from it in support of Muhammad, and has nothing critical to say of it.
Another interesting piece of information is brought out from the Muslims who fled to Abyssinia for refuge. On page 155, the Christians have a discourse amongst themselves. Their ruler asks them, "The what do you say about Jesus?" "We believe that he is the Son of God".
So, even at this time, in the time of Muhammad, Christian people, not far from Mecca, were testifying that Jesus is the Son of God.
Further evidence that Muhammad had gained information about Christianity in Mecca is brought out on pages 163. Some men are having a discourse one man said, "We worship the angels; the Jews worship Uzayr; and the Christians worship Jesus Son of Mary."
The theology about Jews worshipping Uzayr (Ezra) is incorrect - real Judaism never worshipped Ezra. This concept of calling Ezra could have emanated from a heretical Jewish branch. However note that this theological mistake made its way into the Quran (9:30). Again, we see evidence of borrowing, and referring to local myth, we do not see evidence of real "revelation" from God.
If they - the Meccans, knew the Christians worshipped Jesus, wouldn't Muhammad have also known it? Remember, they knew it without the need of "revelation".
Here is some relevant information on Jesus being the Unique Son of God.
Earlier in this paper, Margoliouth was quoted. He mentioned Muhammad spending time with a Christian or Jewish slave, and another Jewish slave in Mecca. Ibn Ishaq also provides some detail. Here is the quote from page 180:
"According to my information the apostle used often to sit at al-Marwa at the booth of a young Christian called Jabr (2), a slave of B. al-Hadrami and they used to say "The one who teaches Muhammad most of what he brings is Jabr the Christian, slave of the B. al-Hadrami." Then God revealed in reference to their words "We well know that they say, "Only a mortal teaches him"." The tongue of him at whom they hint is foreign, and this is a clear Arabic tongue. (3)
END OF QUOTE
Note (2) says, "Noldeke, Der Islam, v (1914), 163 was of the opinion that this man was an Abyssinian slave, the name Gabru (Gabre) meaning "slave of" in Eth.
Note (3) says, Sura 16:105
For the sake of brevity, I will note that in Yathrib, i.e. Medina, there were several tribes of Jews. They had their rabbis, priests and they had the Torah. On page 253, it says,
"When the war came to an end they (the Jews) ransomed their prisoners in accordance with the Torah..."
The war was a war between two pagan tribes in Medina. One group of Jews helped one tribe, and two groups of Jews helped the other pagan tribe.
Later Muhammad spoke the Quran in reference to these Jews....."Will you believe in a part of the scripture and disbelieve in another part? I.e. would you redeem him in accordance with the Torah and kill him when the Torah forbids you to do so,...."
Clearly then, the Jews in Medina had what Muhammad believed was the Torah.
SIRA AND THE INFANCY GOSPELS
We now come to an interesting quote in the Sira or biographical material. On pages 253 - 254:
"He (Muhammad speaking the Quran) continued: We gave Moses the scripture and We sent apostles after him and We gave Jesus, Son of Mary, the clear proofs," i.e. the signs which were wrought by Him in raising the dead; forming the likeness of birds from clay and then breathing into them so that they became birds by God's permission; healing the sick; and news of many hidden things which they stored in their houses; and His confuting them from the Torah and the Gospel which God had created for Him. ..... And when a scripture comes to them from God (the Quran) confirming what they already have, ......"
Here two things stand out relevant to the topic:
1) Muhammad is now quoting from an Infancy Gospel. More on that later.
2) Muhammad said that his Quran "confirms" the Scripture that the Jews have.
MUHAMMAD, THE RABBIS, AND THE STONING
Ibn Ishaq also recorded Muhammad's interaction with a group of Jews in Medina. On page 266...
"Ibn Shihab al-Zuhri told me that he heard a learned man of Muzayna telling Said Musayyab that Abu Hurayra had told them that Jewish rabbis had gathered in their school when the apostle came to Medina. A married man had committed adultery with a married woman and they said: "Send them to Muhammad and ask him what the law about them is and leave the penalty to him. ...The prophet walked to meet the rabbis in the school house and called on them to bring out their learned men and they produced Abdullah Suriya.
END OF THIS PORTION OF THE QUOTE
We see that Muhammad interacted with a group of Rabbis. Not only that, they had their own school! So here, in Medina, was a Jewish theological school.
Muhammad then ordered that the adulterers be stoned.
IBN ISHAQ CONTINUED page 267
"Then He said: "They change words from their places, saying, If this be given to you receive it, and if it is not given to you, i.e. the stoning, beware of it. "
We see from the above that this verse in the Quran is related to a specific group of Jews playing tricks on the Muslims. It clearly does not say that the Torah was corrupted.
IBN ISHAQ CONTINUED
"When the apostle gave judgment about them he asked for a Torah. A rabbi sat there reading it having put his hand over the verse of stoning. Abdullah Salam struck the rabbi's hand saying "This, O prophet of God, is the verse of stoning which he refuses to read to you." The apostle said, "Woe to you Jews! What has induced you to abandon the judgment of God which you hold between your hands?" .....The apostle said, "I am the first to revive the order of God and His book and to practice it."
Here Muhammad clearly confirms the authenticity of the Torah. The Jews held it between their hands. Muhammad even went so far as to say he was practicing the Torah!
Another revealing discourse takes place between some Jews and Muhammad.
"Rafi Haritha and Sallam Mishkam and Malik al-Sayf and Rafi Huraymila came to him (Muhammad) and said: "Do you not allege that you follow the religion of Abraham and believe in the Torah which we have and testify that it is the truth from God?" He replied, "Certainly, but you have sinned and broken the covenant contained therein and concealed what you were ordered to make plain to men, and I dissociate myself from your sin."
Again, Muhammad, in no uncertain terms affirms the Torah which the Jews had in their possession in Medina!
MUHAMMAD, THE INFANCY GOSPEL, AND THE CHRISTIANS FROM NAJRAN
On pages 270, 271 of Ibn Ishaq, Christians from Najran visit Muhammad. Ibn Ishaq notes that they were affiliated with the Christians of Byzantium.....
"A deputation from the Christians of Najran came to the apostle. There were sixty riders, fourteen of them from their nobles of whom three were in control of affairs.....
Abu Haritha occupied a position of honor among them and was a great student, so that he had an excellent knowledge of their religion, and the Christian kings of Byzantium had honored him and paid him a subsidy and gave him servants, built churches for him and lavished honors on him, because of his knowledge and zeal for their religion."......
"They were Christians according to the Byzantine rite, thought they differed among themselves in some points, saying He is God; and He is the son of God; and He is the third person of the Trinity, which is the doctrine of Christianity. They argue that he is God because he used to raise the dead, and heal the sick, and declare the unseen; and make clay birds and then breathe into them so that they flew away (sura 3:43) and all this was by the command of God Almighty, "We will make him a sign to men (sura 19:21). They argue that he is the son of God in that they say he had no known father; and he spoke in the cradle and this is something that no child of Adam has ever done. They argue that he is the third of three in that God says; We have done, We have commanded, We have created and We have decreed, and they say, If He were one he would have said I have done, I have created, and so on, but He is He and Jesus and Mary. Concerning all these assertions the Quran came down."
END OF QUOTE
One important item to note is that the Najran Christians were affiliated with Byzantine Christians.
I want to point out here the error in the Quran concerning the Trinity is also repeated here in Ibn Ishaq's work. The Christians are talking ...
"...If He (God) were one he would have said I have done, I have created, and so on, but He is He and Jesus and Mary. Concerning all these assertions the Quran came down."
What Ibn Ishaq is saying is that the Quran was responding to these Christians' erroneous statements about the Trinity.
Pages 272-277 is Ibn Ishaq's Tafsir on Sura 3. On pages 275 - 276, we find reference to the Quran quoting from the Infancy Gospels. More on that later.
Finally, I will note that in the Kaba, there were pictures of Jesus in Mary. Page 552 says:
"I.I. from Hakim b. Abbad b. Hanif and other traditionalists: Quraysh had put pictures in the Kaba including two of Jesus son of Mary and Mary. I. Shihab said: Asma Shaqr said that a woman of Ghassan joined in the pilgrimage of the Arabs and when she saw the picture of Mary in the Kaba she said, "My father and my mother be your ransom! You are surely an Arab women!" The apostle ordered that the pictures should be erased except those of Jesus and Mary"
Tisdall has an illuminating comment on the Jews Muhammad dealt with,
"Although the Arabian Jews doubtless possessed copies of their Holy Books, they were not distinguished for learning, and then, as now for the most part, they practically gave greater heed to their Rabbinical traditions than to the Word of god. It is not surprising therefore to find litle real knowledge of the Old Testament in the Quran, though, as we shall see, it contains a great deal of Jewish legend." "The Sources of the Quran, pages 61, 62. 
Of course, all the above proves that there was a Christian presence in Mecca and Medina. Since Christians also believe the Torah, they could have informed Muhammad of both the Torah and Gospel teachings, stories, and related material, fabricated or true. Muhammad could have learned from the many sources available to him and repeated the stories as the Quran.
Fundamentalist Muslims have objected to scholar's claims that Muhammad borrowed from other religions. They present a number of red-herring, straw man, or purposely ignorant arguments to obscure the facts of the Christian presence in Mecca.
Here are some of their arguments.
A1) "Muhammad was illiterate, he couldn't read and write, so how could he possible borrow from Jewish and Christian books and Scriptures?"
ANSWER: There was a time in Muhammad's life when he could do some reading and writing. Reference Bukhari's Hadith's 4.288.
Here Muhammad asked for pen and paper for writing. While the debate of whether or not Muhammad could read can go on, or at what time he learned how to read and write, it really has no bearing on the argument. Muhammad could have listened to the Christians and Jews reciting their Scripture, or teaching him, and he could have remembered what they said and later repeated it as the Quran.
Judging from the meager citations concerning Jesus et. al. in the Quran, it would have been quite easy for anyone with an average memory to remember and quote those details.
Also note that this fundamentalist Muslim argument is not new. Tisdall encountered it about 100 years ago. His response is given on pages 130, 131, of "The Sources of the Quran" . I'll quote part of his answer: "The parallels which we have drawn between certain passages in the Quran and those resembling them in various Jewish writings are close enough to show the ultimate source of much of the Quran. But in no single case are the verses of the Quran translated from any such source. The many errors that occur in the Quran show that Muhammad received his information orally, and probably from men who had no great amount of book-learning themselves.
A2) Some Muslims ask: "So how was Muhammad borrowing from the Bible when the non-existence of any Arabic Bible or Arabic apocryphal sources has been proven?"
ANSWER: From the above quotes from the Quran, Hadith, and Sirat, I've shown that there was an abundance of written material for him to reference. Also note, that the Quran did not have to borrow from the Bible. It actually borrowed more from the New Testament Apocrypha (Infancy Gospels) than the actual New Testament. Finally, Muhammad did not have to read the borrowed religious material in order to use it. He only had to have heard someone teach it. And, this was clearly detailed in the Hadith - the Jews read the Torah in Hebrew and explained it to the Muslims. Additionally, Ibn Waraqa, Muhammad's brother in law, did write "Gospel" material in Arabic.
A3) Some Muslims assert that since there was no "seat" of Christianity or Judaism in the Hijaz then Muhammad could not have learned about those religions.
ANSWER: It's already been shown that there was plenty of written material, some in Arabic, in the Hijaz during Muhammad's time. Further, the fact that there was no seat of Christianity in the Hijaz supports the fact that the Arab tribes there were more removed from the true Gospel, and more subject to folk tales. This is borne out by the amount of folk takes found in the Quran! The Quran has an amazing lack of substance when dealing with doctrinal Christian topics. Why? Because Muhammad did not hear about them. He primarily hear tales from people who were removed from actual "seats" of Christianity.
A4) Muhammad himself addressed the Meccan's claims that he learned his revelations from someone else. In his Quran Muhammad said:
"We know indeed that they say "It is a man that teaches him." The tongue of him they wickedly point to is notable foreign while this is Arabic pure and clear. Those who believe not in the Signs of Allah, Allah will not guide them and theirs will be a grievous Penalty. [Quran 16:103-104]"
Muslims then argue that had someone been teaching Prophet Muhammad(P), his family and close friends would have eventually known. However, far from being skeptical about his claims to prophethood, these people gave their wealth and lives for Islam.
ANSWER: Since Muhammad wanted the Meccans to believe that he was a prophet who actually received revelations from God, it follows that he would have denied that he learned his material from others. Perhaps he felt some strange sensation when he repeated other's material, and thus believed it was actually revelation. Perhaps he simply repeated it as his own. Either way, he claimed the "revelations" were his own to preserve his credibility.
Note that even the Quran admits that the Meccans were able to point to a foreigner who was communicating with Muhammad. As Torrey pointed out
"Mohammed does not deny the human teacher, but only insists that the teaching came down from heaven."
Why did his family and friends follow him? Were they aware of others teaching him? Perhaps, perhaps not. It doesn't matter if they knew or not. Muhammad learned much of his knowledge well before he began to speak the Quran. Having family and friends following a person who claimed to be a prophet is not extraordinary. Joseph Smith did much better than Muhammad. Hindu "Gurus" have had family followers through the centuries. There have always been people claiming to be "prophets" or blessed with some special revelation or knowledge who have had followers to the point of death. Muhammad's followers were initially poor, uneducated people from the lower rungs of society. His own tribesmen rejected him from the start.
A5 Another Muslim argument against borrowing is "Similarity does not mean borrowing."
Their argument basically states that different "prophets", such as Abraham, Noah, Moses, etc. were given different commandments and words from God. Would one group of followers accuse the others of "borrowing"? No, instead the reply would be:
a) The Law has come from the same source (from the one and only God),
b) Any differences from absolute similarities would mean correction of the message that got corrupted,
c) Any other differences would mean additional Law with the newer revelation,
I agree that similarities do not necessarily mean that material was borrowed. Recently, an American, Russian, and Indian all shared in the Nobel Prize for physics. They had independently worked on the same research and reached similar results. The Nobel committee recognized their individual efforts and awarded them all a share of the prize.
The Muslim argument is similar. On the surface it sounds like a plausible argument on behalf of the Quran and Islam; Muhammad was just another prophet in the line of the prophets, who was receiving independent revelation. They continue that the Rabbinical stories found in the Mishnah were true, and that they were revealed by the Quran.
However, their example and argument don't hold up well with just a little scrutiny. First of all, the material that Muhammad was accused of borrowing was already know as fable, or someone else's religious writings (i.e. the Mishnah). So, mixed in the Quran were jaded "revelations", i.e. folk tales and myths. People knowledgeable in Muhammad's time said the same thing you and I would say if we heard someone recite "Sleeping Beauty" (the Seven Sleepers) as revelation! "It's a myth!".
Likewise, even the Islamic stories don't hold up to Jewish fables or history. For instance, in the Islamic story, Abraham and Nimrod interact. But according to Jewish history, Nimrod lived many generations before Abraham's time.
If one of the scientists would have presented another's work, work that was known, the Nobel committee would have said he plagiarized material and he would not have won anything. His name would have been disgraced. Muhammad plagiarized other's material.
Additionally, I think that while God can give revelation as He sees fit, He doesn't give Aesop's Fables as revelation.
Second of all, God would not give revelations that contradict each other. The New Testament and Old Testament, agree with each other. But the Quran contradicts them both. For example, the Quran gets Abraham's father's name wrong. The Quran also gets the people who died in Noah's flood wrong. Etc., etc., etc. God is not the author of confusion, therefore He is not the author of the Quran.
BADAWI'S SIX QUESTIONS
One prominent Muslim apologist - Jamal Badawi - has put forth six questions that he assumed were very challenging. Actually, the questions are fairly easy to answer. I'll follow my answers to his questions by asking six questions.
Here are Badawi's six questions:
Q1) Why is it in spite of the abundance of historical material on Muhammad's life, and in spite of the extensive research on his life for centuries by his severe critics, that it was not possible to discover the mysterious teacher(s) through whom Muhammad might have learned all that?
A1) "Mysterious teacher(s)"!? Not at all. I've presented a variety of Islamic sources that all detail Muhammad's interactions with Jews, Christians, pagans, etc. There were never "mysterious teacher(s)". The culture of the Hijaz had been touched with knowledge of Christianity and Judaism. Muhammad naturally learned of some Christian and Jewish teachings through contact with these various people.
RQ1) My response question: Are Muslims so ignorant of the history of their head honcho that they cannot realize and admit that he had a great deal of contact with followers or people who were somewhat knowledgeable of Christianity and Judaism?
Q2) It is known that Muhammad was opposed, ridiculed and persecuted for nearly 13 years by his own contemporaries. With this magnitude of severe enemies, was it not possible for them to prove to the masses that Muhammad's claim of revelation was sheer fabrication? Was it not possible for them to reveal and name the person whom they alleged to be the human source or sources of his teachings? Even some of his adversaries who had made this assertion, changed their minds later on and accused him, instead, of magic or being possessed by evil... etc.
A2) His contemporaries did prove to the masses that Muhammad claim of revelation of sheet fabrication. Only a handful of people from Mecca actually became his followers out of choice. Mecca only submitted to Muhammad when he had an army of some 12,000 soldiers outside of the city. Before that, Muhammad was almost totally rejected. It was compulsion & conquest that caused the Meccans to accept Muhammad. Previously they had exposed some of Muhammad's teachers. The Christian slave Jabr, Bahira the Monk, Ibn Waraqa, ext. All of these people spoke with Muhammad and shared religious knowledge with him. And as far as his accusers saying he was "possessed by evil", or demon possessed, they probably believed that he had both gained religious knowledge from others, and that he was demon possessed.
RQ2) My response question. If Islam were true, why was so much violence needed to establish it? Why did Muhammad teach that those who leave Islam are to be murdered? Why did Muhammad have to have slave girls killed for laughing at him? Why did Muhammad have to extort money from Christians and Jews when his people were so poor? Were was this "truth"? Or, as Muhammad believed, was "Allah" providing material wealth for the Muslims by taking it by force from others?
The multitudes followed Jesus by choice, not force. The early church grew through peaceful means, not conquest. If Islam is true, why the constant presence of brutal force to keep it established?
Q3) Muhammad(P) was raised among his people and every aspect of his life was exposed to them, especially by the openness that characterizes tribal life in the desert. How could the multitudes of his contemporaries, including many of his close relatives who knew him so well, how could they believe in his truthfulness if they had any doubt that he was claiming credit for ideas taught to him by some other teachers without bothering to give them credit ?
A3) This was already answered earlier. Basically, "the multitudes" did not believe in his truthfulness. Even his clan rejected him. Some of his family did believe him, only a few. But this is not notable. Joseph Smith has had family followers, so have Hindu Gurus, etc. Having a few members of your family believe in you does not constitute a proof for prophethood.
RQ3) Why did the multitudes who personally knew Muhammad reject him? Did they believe him to be a liar, or a lunatic, or both? Most of the people who had intimate contact with Jesus became His followers. Only a handful of people who had intimate contact with Muhammad accepted him - His clan rejected him almost wholesale.
Q4) What kind of teacher might have taught Muhammad(P) a coherent and complete religion that changed the face of history? Why didn't he or they (if any) speak against the alleged student who continued learning from them, while ignoring them and claiming some other divine source for his teachings?
A4) Islam is not a coherent and complete religion. Allah even had to abrogate the verses he gave to Muhammad, or cause him to forget them while he slept. Allah could not even make up his mind in 8:65 vs. 8:66! If this were such a coherent religion, why were Ali and Aisha trying to kill each other just a few years after Muhammad's death? What about muta marriage? What about eating donkey meat? Why did Muhammad need special "revelations" just to marry his adopted son in law's wife? Why did Muhammad need special "revelations" to have Allah tell Muhammad to break his vows? Why is there so much "on again, off again" in Islam? If this were such a complete religion, why did Abu Bakr have to launch major wars against those who no longer wanted to be Muslims? Couldn't the religion stand on it own without armies forcing it upon others?
Q5) How could many Jews and Christians amongst his contemporaries become Muslims and believe in his truthfulness if they knew he was copying from their scriptures or learning from their priests or rabbis?
A5) This question is based upon an erroneous premise. The opposite of what is assumed is true. Only a few Jews became Muslims. In fact, Muhammad put to death and enslaved practically an entire tribe of Jews. Less than a dozen became his followers. That pales in contrast to the 800 men and teens he had beheaded and the several thousand women and children he enslaved. They could have lived if they accepted him as their prophet. Instead, knowing he was a false prophet, they choose death and enslavement. They knew he had copied. They had tested him, and he failed their tests. Consequently, they decided not to risk the truth for falsehood.
RQ5) Since Muhammad was almost totally rejected by the People of the Book, both Christians and Jews, doesn't this prove that he was a false prophet?
Q6) It is known that some of the Quranic revelations to Muhammad(P) in the presence of people. The Quran was revealed over the span of 23 years, where then that was mysterious, perhaps invisible teacher of Muhammad(P)? How could he have hidden himself for so long? Or how could Muhammad(P) who was constantly surrounded by companions, how was he able to make frequent secret visits to that mysterious teacher or teachers for 23 years without even being caught once?
A6) Again, this question is based upon erroneous premises. There was never a "secret" teacher, or at least there was no need of one. Muhammad's initial knowledge of Judaism and Christianity was meager, and the few things he knew could have easily been remembered. As time went on, his interactions with others would have allowed him to learn more, both in amount and in detail. Thus the Quranic verses provide more detail at times than others. Much of the Quran is repetitious, or mere invectives against his enemies or the Jews that rejected him. There is nothing noteworthy in that.
RQ6) There is abundant evidence that Muhammad was in contact with members of other religions. There is evidence that Muhammad was told stories from other religions. There is evidence that Muhammad repeated stories that were established as myths, or other people's religious writings. Are you willing to stake your eternity upon someone who borrowed other religious writings?
I've presented evidence that Muhammad had a certain amount of exposure to Christian and Jewish people and their teachings. Muhammad heard and learned, via word of mouth, their religious stories from his childhood onward. He grew up with them in Mecca. And I've presented evidence that Muhammad repeated several of the stories he heard, as the Quran.
When one takes into account the actual material that Muhammad cited in reference to Jesus, there is a paucity of material. A few stories about John the Baptist's family, a few stories about Jesus and Mary, and a few redundant stories about Moses, Aaron, and Abraham. All in all, it fills no more than a few pages. Muhammad had years to learn Christian and Jewish material. His culture was influenced by those religions. Before he began preaching Islam he had on many occasions dialoged with People of the Book. It would have been easy for anyone, with a keen interest, to have learned the meager religious details Muhammad repeated in the Quran.
Muhammad referred to the material he learned as the Torah and Gospel. He may have heard authentic Gospel material, and / or most definitely he learned simple Apocryphal material; but he was ignorant and none the wiser when it came to knowing truth from myth.
Muhammad quoted material from these spurious Gospels and recited them as the Quran. These Gospels have their source in folklore and were never accepted by the Church as Scripture from the earliest times. Muhammad unknowingly recited myth as "revelation" from God. These myths he learned from various Christian, Jewish or others who had learned them elsewhere and likewise taught Muhammad.
Muhammad did borrow from other religions. Whether he re-worked them in his mind and mixed them with his personal interpretation, or whether he copied the stories he heard wholesale is not relevant; what is relevant is that he borrowed.
I'll end with a powerful quote from Tisdall, pages 279, 280 from "The Sources of Islam", 
"All this being considered, it is clear that, although Muhammad borrowed religious practices, beliefs, and legends from various different sources, yet he combined them in some measure into one more or less consistent whole, thus producing the religion of Islam. Some parts of this are good, and Islam contains certain great truths, borrowed from other systems of religion, which in a measure account for its continued existence in the world. But is certainly does not contain a single view or lofty religious conception, and its general tone is all to faithful a reflection of the carnal and sensual nature of its founder. To use an Oriental simile is not perhaps inappropriate in speaking of such a thoroughly local and Oriental religion as Muhammadanism. Islam therefore may aptly be compared with: "That bituminous lake where Sodom Flamed," which, receiving into its bosom the waters of many streams that, thus united, assume the shape and form of its basin, turns them all into one great widespread Sea of Death, from whose shores rise pestilential exhalations destructive to all life within reach of their malign influence. Such is Islam. Originating from many different sources and receiving into it certain elements of truth, it has assumed its form from the character and disposition of Muhammad; and thus the good in it serves only to recommend and preserve the evil which renders it a false and elusive faith, a cure to men and not a blessing - one that has turned into deserts many of the fairest regions of the earth, that has, even in our own days, deluged many a land with innocent blood, and has smitten with a moral, intellectual, and spiritual blight every nation of men which lies under its iron yoke and groans beneath its pitiless sway."
1 Yusef Ali, "The Holy Quran", Amana Publications 1989
2 Encyclopedia Britannica, under "Islam".
3 Ignaz Goldziher, "Muslim Studies", State University of New York Press, Albany.
4 Arthur Jeffery, "The Foreign Vocabulary of the Quran", Oriental Institute of Baroda, 1938.
5 D. S. Margoliouth, "Muhammad and the Rise of Islam", G.P. Putnam and Sons.
6 J. S. Trimingham, "Christianity Among the Arabs in Pre-Islamic Times", Longman Group Limited, London, 1979.
7 Ali Dashti in "23 Years: A Study of the Prophetic Career of Mohammad", Mazda Publishers, Costa Mesa CA, 1994.
8 Theodor. Noldeke "Geschichte des Qorans", quoted by Ibn Warraq in "The Origins of the Quran", Prometheus Books.
9 Abraham Geiger, "Judaism and Islam", KTAV Publishing House, New York, 1970.
10 Alan Jones, "The Koran", Everyman, London, 1992.
11 Richard Bell, "Introduction to the Quran", Edinburgh University Press, 1953.
12 Richard Bell, "The Origin of Islam in its Christian Environment, Frank Cass & Co LTD, London, 1968
13 William Muir, "Mahomet and Islam, Fleming Revell Company.
14 W.M. Watt, "Muhammad at Mecca", Oxford University Press, London 1952.
15 W.M. Watt, Muhammad at Medina, Oxford University Press, London, 1956.
16 Maxime Rodinson, "Muhammad", Penguin Books.
17 Alfred Guillaume, "Islam", Penguin Books.
18 H.A.R. Gibb, "Mohammedanism an Historical Survey", Oxford University Press, NY
19 W. St. Clair Tisdall, "The sources of Islam", T & T Clark, Edinburgh, Scotland.
20 Charles Torrey, "The Jewish Foundation of Islam", KTAV Publishing, New York
21 N. J. Dawood, The Koran, Penguin.
22 Dr. William Campbell, "The Quran and the Bible in the Light of History and Science", MER.
23 Sahih al-Bukhari, translated by Muhsin Khan, Kitab Bhavan, New Delhi, India
24 Sunan Abu Dawud, translated by Ahmad Hasan, Al-Madina Publications, New Delhi, India
25 A. Guillaume, "The Life of Muhammad", a translation of Ibn Ishaq's "Sirat Rasul Allah", Oxford University Press, Karachi, Pakistan.
26 Ibn Sa'd, "Kitab al-Tabaqat al-Kabir", (Book of the Major Classes), translated by S. Moinul Haq, Pakistan Historical Society.
27 Herbert Danby, "The Mishnah", Oxford University Press.
28 Dr. H. Freedman & Maurice Simon, (editors) "Mishnah Rabbah", Genesis (Noach) (CH 38:11-13) Vol. 1, pp. 310 -311, Soncino Press London.
29 al Tabari, "Ta'rikh al-rusul wa'l-muluk", (The History of al-Tabari), vol. 4, translated by Moshe Perlmann, State University of New York Press.
30 J. K. Elliot, "The Apocryphal New Testament", (editor) Oxford.
31 M. R. James "The Apocryphal New Testament", Oxford.
32 Helmut Koester, "Ancient Christian Gospels", Trinity Press International.
33 E. Hennecke, "New Testament Apocrypha", edited by W. Schneemelcher, translated by R. McL. Wilson, published by Lutterworth.
34 E. Hennecke, "New Testament Apocrypha", edited by Schneemelcher, translated by R. McL, Wilson, published by WJKP.
35 Jacques Hervieux writes, "The New Testament Apocrypha", published by Hawthorn Books
36 St. Clair Tisdall "The Original Sources Of The Quran", published by Society For The Promotion Of Christian Knowledge, London.
37 St. Clair Tisdall, "The Sources of the Quran", Society For The Promotion Of Christian Knowledge, London.
MUHAMMAD THE BORROWER - THE SCHOLARS
In the introductory paragraph, I referred to various scholars who state that Muhammad borrowed religious material. These scholars and Muhammad's contemporaries believed that Muhammad borrowed material from various religious writings because the Quran, Hadith, and Sirat all contain quotes, near-quotes, and misconstrued quotes from them.
Supporting their assertions are Islamic source materials show that Jews and Christians were in contact with Muhammad from his childhood onward, and that they lived in areas near Mecca. It was not only material from their Holy Books that Muhammad borrowed from, he also borrowed material from secondary sources such as New Testament Apocrypha, Mishnah, Talmud, etc. Either by direct association, or through word of mouth, Muhammad learned their religious stories. See parts 2 and 3 for these details.
Let me quote just a few scholars and the Encyclopedia Britannica. (Caps are mine).
From the Encyclopedia Britannica, under "Islam", page 6.
"Thus the Quran often gives the impression of having been produced by a rather haphazard method of composition, an impression that is further heightened by the fact that certain favorite phrases such as "but God is forgiving, compassionate," "God is knowing, wise," "most of them know nothing" often have little or no apparent connection with the immediate context. In fact, some skeptics claim that these additions served only to produce a needed rhyme. ..... Also the vocabulary of the Quran is overwhelmingly of Arabic origin, but there are, nevertheless, borrowed words, mostly from Hebrew and Syriac, bearing witness to Muhammad's debt to Judaism and Christianity. These loan words are primarily technical terms such as injil, "gospel", (Greek evangelion); taurat, "the law", or Torah", of Judaism, Iblis, "the Devil" (Greek diabolos); or translations or adaptations of theological terms such as amana, "to believe" (Hebrew or Aramaic); salat, "prayer" (probably Syriac). Such explanations are usually regarded with suspicion by Muslims, since orthodox doctrine holds that the language of the Quran is the purest Arabic."
The Encyclopedia continues on page 9....
"Western Scholars who have analyzed the contents of the various revelation have shown that much of the narrative material concerning biblical persona and events differs from the biblical account and seems to have come from later Christian and above all, from Jewish sources, (e.g. Midrash). Other motifs, such as the idea of the impending judgment and the descriptions of paradise agree with standard topics in the missionary preaching of the contemporary Syriac church fathers. THE DEPENDENCE NEED NOT, HOWEVER, BE OF A LITERARY KIND, BUT MIGHT BE DUE TO INFLUENCE FROM ORAL TRADITIONS." 
NOTE: at the end it notes that Muhammad could have learned not only from a manuscript, (being taught from a Hebrew, Arabic, Syriac, or Greek religious writing), but from oral teachings as well, i.e., from listening to others relating Jewish, Christian, and other stories.
THE SCHOLAR'S WRITINGS
Ignaz Goldziher writes in "Muslim Studies", page 346:
"The fact that Islam regarded Christianity as a religion from which something could be learnt, and did not disdain to borrow from it, is acknowledged by the Muslim theologians themselves, (1) and the early elements of Hadith literature offer us a great wealth of examples which show how readily the founders of Islam borrowed from Christianity. We do not here allude to those vague borrowings which in the earliest times of Islam, through verbal communications with Christian monks or half-educated converts, helped in building up the form and content of the faith, and which appear in the form of isolated technical expressions, Bible legends, and so forth; but we mean those borrowings which are presented in a more definite shape, and evince a certain, if not a very extensive, knowledge of the Christian Scriptures."
(1) This note says, "Thus Ibn Hajar, I, p. 372, quotes ancient authorities who acknowledge the share which the communication of the Christian proselyte Tamin al-Dari had in the formation of Muhammad's eschatology. [Cf. Tamin al-Dari in the EI (Ency. of Islam)] 
Arthur Jeffery writes in "The Foreign Vocabulary of the Quran", in the forward, page vii:
"Emphasis has been placed in recent years on the too long forgotten fact that Arabia at the time of Muhammad as not isolated from the rest of the world, as Muslim authors would have us believe. There was at that time, as indeed for long before, full and constant contact with the surrounding peoples of Syria, Persia, and Abyssinia, and through intercourse there was a natural interchange of vocabulary. Where the Arabs came in contact with higher religion and higher civilization, they borrowed religious and cultural terms. This fact was fully recognized by the earliest circle of Muslim exegetes, who show no hesitation in noting words as of Jewish, Christian, or Iranian origin. Later, under the influence of the great divines, especially as ash-Shafi'i, this was pushed into the background, and an orthodox doctrine was elaborated to the effect that the Quran was a unique production of the Arabic language. The modern Muslim savant, indeed, is as a rule seriously distressed by any discussion of the foreign origin of words in the Quran.
Jeffery continues on page 1 of the introduction:
"One of the few distinct impression gleaned from a first perusal of the bewildering confusion of the Quran, is that of the amount of material therein which is borrowed from the great religion that were active in Arabia at the time when the Quran was in process of formation. From the fact that Muhammad was an Arab, brought up in the midst of Arabian paganism and practicing its rites himself until well on into manhood, (1) one would naturally have expected to find that Islam had its roots deep down in this old Arabian paganism. It comes, therefore, as no little surprise, to find how little of the religious life of this Arabian paganism is reflected in the pages of the Quran. ....
....it is plain that Muhammad drew his inspiration not from the religious life and experiences of his own land and his own people, but from the great monotheistic religions which were pressing down into Arabia in his day (6).
Note 1 says: "Convincing proof of this is found in the statement of the Prophet quoted in Yaqut, Mu'jam, iii, 664, to the effect that on a certain occasion he sacrificed a ewe to Uzza, which he excuses on the ground that at that time he was following the religion of his people.
Note 6 says: "Noldeke-Schwally, ii, 121, Buhl, EI (Ency. of Islam) ii 1066; Ahrens, Muhammed als Relligiouns-stifter, 22 ff." 
D. S. Margoliouth writes in "Muhammad and the Rise of Islam", page 106: [comments in ( ) brackets are mine]
"The needs of his (Muhammad's) profession do not appear to have made him actually a student - yet there is no question that as the Koran grew in bulk, its knowledge of biblical stories became somewhat more accurate: and thought this greater degree of accuracy may have at times been due to the Prophet's memory, it is more likely that he took such opportunities as offered of acquiring more information. The following story gives us an idea of his method. Jabr, a client of the Banu ' Abd al Dar, was a Jew (1) who worked as a smith in Meccah. He and Yasr (also a Jew) used to sit together at their trade and in the course of their work read out their sacred book the Prophet used to pass by and listen. Presently Jabr was converted by hearing the Prophet read the Surah of Joseph (2). It has been suggested that some of the Christian matter in the Koran may have been learned from an early follower named Suhaib, who was a Greek from Mosul (3). The tradition names more than one person who was thought by the Meccans to be the Prophet's mentor, and the Koran even refutes this charge by stating that the person to whom they allude had a foreign tongue, and could not therefore be the author of an Arabic Koran. Perhaps that reply is unconvincing; but the impression which the Koran leaves is that of information picked up casually rather than acquired by any sort of methodical study (4). In a Surah delivered at Medinah in which the story of Saul should be told, Saul's name is mutilated to Talut, clearly a jingle with Galut, the nearest that the Prophet could get to Goliath: the name of Samuel is forgotten, he is confused with Gideon, and the story of Gideon is told wrongly. This phenomenon almost disposes of the theory of a mentor, for no mentor could be so ignorant of the Bible. Moreover the sources of the Koran are very numerous - Abyssinian, and Syriac, as was as Hebrew and Greek (5) So far then as the biblical tales of the Koran were not reproductions of matter heard by Muhammad on his early travels, they are likely to have been all picked up by listening when services or Bible readings were going on.
(1) Or a Christian; the Moslems are careless about distinguishing.
(2) Isabah, i., 452; Wakidi (W.), 349
(3) Loth in Z. D. M. G., xxxv., 621
(4) Noldeke, Sketches, c. ii
(5) The best evidence for this is the form assumed by the proper names. Syc, Die Eigennamen im Koran, 1903, does scant justice to this theme. 
J. S. Trimingham notes the existence of New Testament apocrypha writings in the Quran by saying in "Christianity Among the Arabs in Pre-Islamic Times", page 211, note 5:
"The Arabic Gospel of the Infancy, derived from Aramaean versions, shows Jesus declaring his divinity from the cradle. This story was among the legends transmitted to Arab Christians, and a form of it appears in the Quran."
Trimingham implies that Muhammad had contact with people who were Christian, or knew Christian or Christian related teachings.
Further, he wrote on page 266:
"The reason why the forms of Arabic words for the Hebrew prophets derive from Syriac and not directly from Hebrew is due to the influence of Christian Arabs on Arab folklore. Not only were Christian apocryphal stories relayed, but even Old Testament patriarchal stories, which Christians did not associate with Jews but with Aramaean religious history." 
Even the Muslim scholar Ali Dashti in "23 Years: A Study of the Prophetic Career of Mohammad", notes Muhammad's interactions with people who were Christian, Jewish, or other. On pages 21, 22 he writes:
"A process of this kind had begun in Mohammad's mind during his childhood and had prompted him to meet and talk with Christian monks and priests on his Syrian journey instead of spending all his time on commercial business. On his way back, through the lands of Medyan and the Ad and Thamud, he had heard the legends of the local people. In Mecca itself he had exchanges visits with followers of the scriptural religions. He had sat for hours in Jabr's shop near the hill of Marwa, and had been in constant touch with Khadija's cousin Waraqa b. Nawfal, who is said to have translated a part of the New Testament into Arabic. All these experiences are likely to have turned the ever-present disquiet in his inner mind into turmoil.
There is a reference in the Qoran to Mohammad's long and frequent talks with Jabr. The Qorayshites alleged that Mohammad had learned the words of the Qoran from Jabr, who was a foreigner. The answer is given in verse 105 of sura 16 (on-Nalh): "And We know that they say, "It is only a human who is teaching him." The speech of the person at whom they hint is outlandish whereas this is clear Arabic speech." The biographies of the Prophet mention several other followers of the scriptures and possessors of knowledge with whom he exchanged visits before the start of his mission, e.g. Aesh, the sage of the Howayteb tribe, Salman ol-Farsi, and Belal the Abyssinian. Abu Bakr also had discussions with him at that time and agreed with him." 
Theodor Noldeke writes in "Geschichte des Qorans", quoted by Ibn Warraq in "The Origins of the Quran", page 43 writes: ( [ ] brackets are mine)
"But the deviations [in the Quran] from the biblical narratives are very marked. Many of the alterations are found in the legendary anecdotes of the Jewish Haggada and the New Testament Apocrypha; but many more are due to misconceptions such as only a listener (not the reader of a book) could fall into. The most ignorant Jew could never have mistaken Haman (the minister of Ahasuerus) for the minister of Pharaoh, or identified Miriam the sister of Moses with Mary (=Miriam) the mother of Christ.
Below is a link to Muhammad's error concerning Mary being Aaron's sister. This error is in the Quran
In addition to such misconceptions there are sundry capricious alterations, some of them very grotesque, due to Muhammad himself. For instance, in his ignorance of everything out of Arabia, he makes the fertility of Egypt - where rain is almost never seen and never missed - depend on rain instead of the inundation of the Nile (xii 490. The strange tale of "the horned" (i.e., Alexander the Great, xviii. 82 sqq.) reflects, as has been lately discovered, a rather absurd story, written by a Syrian in the beginning of the sixth century; we may believe that the substance of it was related to the Prophet by some Christian. Beside Jewish and Christian histories, there are a few about old Arabian prophets. In there he seems to have handled his materials even more freely than in the others.
The opinion has already been expressed that Muhammad did not make use of written sources. Coincidences and divergence alike can always be accounted for by oral communications from Jews who knew a little and Christians who knew next to nothing. Even in the rare passages where we can trace direct resemblance to the test of the Old Testament (comp. Xx1.105 with Ps. xxxvii. 29; i.5 with Ps. xxvii. 11) or the New (comp. Vii.48 with Luke xvi.24; xlvi. 19 with Luke xvi.25), there is nothing more than might readily have been picked up in conversation with any Jew or Christian. In Medina, where he had the opportunity of becoming acquainted with Jews of some culture, he learned some things out of the Mishna; e.g. v.35 corresponds almost word for word with Mishna Sanh. iv.5; compare also ii.183 with Mishna Ber. i. 2. That these are only cases of oral communication will be admitted by anyone with the slightest knowledge of the circumstances." 
Abraham Geiger documents in "Judaism and Islam" that Muhammad wanted to borrow from Judaism, that he had opportunity to borrow from Judaism, and that it was compatible with his plans to borrow from Judaism. Thereafter Geiger lists and comments upon dozens of themes that Muhammad borrowed form Judaism.
One quote from Geiger is presented here from page 17:
"The possibility of borrowing from Judaism lay for Muhammad, partly in the knowledge which might be imparted to him by word of mouth through intercourse with the Jews, and partly in personal knowledge of their Scriptures; while allowing him the first source of information, we must deny him the second." 
Alan Jones writes in his introduction to Rodwell's translation of the Quran in "The Koran", on page xxv:
"Orthodox doctrine renders discussion of the sources of the Quran irrelevant for Muslims: the Quran is the word of God. They are also able to dismiss discrepancies between the Bible and the Quran by recourse to the doctrine that if there are differences between the Jewish, Christian and Muslims versions of the Scripture the Jews and the Christians have mangled the message and Muslims have not. This doctrinal stance is, however, not without its problems. It is difficult to reconcile the very specific references to, for example, Muhammad's family (cf., for example, Q. 33:28-33) with the belief that each prophet has received the same message.
For non-Muslims the Muslim standpoint is untenable, and non-Muslim scholars have given much thought to the question of how Muhammad might have acquired his knowledge of the Bible. The most commonly accepted view is that Muhammad received most of his information about biblical stories through informants who talked to him; that this material was digested, meditated on and then absorbed into what became the text. There are two passages in the Quran itself that support this view. The first is Q. 16:103: "We also know that they say, "Surely, a certain person teacheth him". But the tongue of him at whom they hint is foreign while this is in plain Arabic." Secondly, Q. 25:4 reads: "And the infidels say "This is a mere fraud of his own devising, and others have helped him with it, who had come hither with outrage and lie"." The allegation of fraud is strongly denied in Q. 25:6: "Say, "He hath set it down Who knoweth the secrets of Heaven and Earth.""; but the question of help is ignored. It should be added that there is some corroboration in Hadith that Muhammad received stories and information from various individuals, including Jews and Christians, and that the material he received from them found its way into Quranic form." 
Richard Bell writes in "Introduction to the Quran", page 161,
"It is the narrative portions of the Quran that its dependence upon the Bible, especially upon the Old Testament, is most evident.....the great bulk of material which Muhammad used to illustrate and enforce his teaching was derived form Jewish and Christian sources, and was meant to reproduce what was contained in the revelation given to the People of the Book"
And on page 163,
"Examination of these parallels to Biblical narratives shows that they were not taken directly from the Bible. It must, of course, be remembered, that Muhammad was never simply a borrower. Material which came to him from outside sources was always made his own, molded by reflection, and freely used for his own purposes....
....it is still clear hat the material did not come to him from literary sources.
Page 164 (comments mine)
"In fact, the whole choice of material (borrowed religious material found in the Quran) is such as to suggest that it came from the memories of men and was communicated to him orally." 
Bell also wrote in "The Origin of Islam in its Christian Environment", pub by Cass, page 100:
"In the previous lecture, the independence of Muhammad was insisted on. That, however, had reference to the beginnings of his mission. It was not intended to deny, what is indeed undeniable, that there was a great deal of direct influence exerted upon him by Judaism and Christianity, and that much of the Quran is directly dependent upon the Bible, and stories associated with the Bible."
And on page 110:
"The stories of the Virgin Mary and the Birth of Jesus appear among them quite on the same footing as the others. These are related, however, not as in the New Testament, but more in the form in which they appear in Apocryphal Gospels. (They have most similarity with the Protevangelium Jacobi, a book that we know to have been widely diffused in the East.) 
William Muir writes in "Mahomet and Islam", pages 37, 38:
"It was in the seventh year of the ministry of Mahomet that the children of Hashim entered the quarter of Abu Talib. There for three years, in virtual confinement, they remained. The wailing of the little ones could be heard from without. The hearts of many were softened at the privations which the ban occasioned; but relief was long of coming.
It must have been about this period that Mahomet obtained a closer acquaintance with Jewish history and tradition, either form those he met at the season of pilgrimage, or from some Hebrew captive detained at Mecca. The Coran begins to teem with lengthy narration of the Creation, Fall, Flood, &c., as also of the patriarchs, kings and prophets, all betraying an intimate acquaintance with Jewish lore......We meet with little or no mention of Christianity in the Suras yet put forth." 
W. M. Watt, in "Muhammad at Mecca", page 26, writes in discussing "sources" for the Quran"
"They (Western Islamic Scholars) have made a fetish of literary dependence, and have forgotten that literary dependence is never more than one side of the picture; there is also the creative work of the poet, ......."The Quran, however, makes explicit statements about the beliefs of the pagan Arabs and about certain ideas which have been passing through the mind of Muhammad and the Muslims.......Then it would be possible to ask to what extent Judaeo-Christian influences could be traced there."
And on page 27:
"These premonitions of monotheism among the Arabs must have been due mainly to Christian and Jewish influences. The Arabs had many opportunities of contact with Christians and Jews. The Byzantine empire, whose power and higher civilization they greatly admired, was Christian, and so was Abyssinia. Even in the Persian empire Christianity was strong, and al-Hirah, the Persian vassal-state with which the Arabs were much in contact, was an outpost of the East Syrian or Nestorian Church. This combination of monotheism with military and political strength and a higher level of material civilization must have impressed the Arabs greatly. The nomadic tribes and settled communities in closest contact with these states were indeed being gradually Christianized; and even some of the Meccan merchants were not uninfluenced by what they saw when they traveled to the border market town on business. There were also Christians in Mecca, traders and slaves (2), but the influence of isolated individuals was probably not so important.
The opportunities for contact with Jews were not so extensive as those with Christians, but some were probably more intimate. This was especially so in Medina where Jews and pagan Arabs were settled side by side. There were also quite a number of Jewish tribes settled at oases in Arabia and in the fertile parts of southern Arabia, either refugees of Hebrew race or Arab tribes which had adopted Judaism. There were apparently practically no Jews in Mecca.
When one turns to questions of detail, one finds that the particular Jewish and Christian groups which influenced the Arabs must have had many strange ideas. By this is not meant the technical heterodoxy of the East Syrians (Nestorians) and the Syrian and Abyssinian Monophysites; the expressions of the leading doctors of these churches were sober compared with many of the extra-ordinary ideas, derived from apocryphal gospels and the like, that seem to have been floating about Arabia. The passage of the Quran which suggests that the Trinity consists of Father, Son, and Virgin Mary is doubtless a criticism of some nominally Christian Arabs who held this view. On the Jewish side, too, much of the detail came not from the sacred Scriptures but from secondary sources of various types.
The possibility of influence from monotheistic groups other than Jews and Christians cannot be entirely excluded, but at most it must have been slight.
And from his "Excursus B", pages 158, 159, Watt writes:
"Thus sound scholarship as well as the theological impartiality of the historian suggests that the chief question to be asked in this field is the extent of Jewish and Christian (and perhaps other) influences upon the Meccan of A.D. 600, not upon Muhammad himself, or rather, upon the Quran; and to this question the answer can be neither simple nor absolutely certain......
The chief piece of evidence is the reference to a teacher of foreign speech in Surat an-Nahl (16:105). Torrey, who makes much of this point (43 f., &c.) notes that Muhammad does not deny having a "human teacher but only insists that the teaching came down from heaven. Now on the supposition that Muhammad had such a teacher, he would most naturally be connected with something which appears to be a fact, namely, the growth in accuracy of the acquaintance with Old Testament stories observable in the Quran. For example, in 37.135 c and 26.171 e(d) the member of Lot's party not delivered is an old woman; elsewhere it is Lot's wife......If there were only one or two instances of this sort of thing they could easily be explained away; but there are a great many; and the Western critic therefore finds it difficult to resist the conclusion that Muhammad's knowledge of these stories was growing and that therefore the was getting information from a person or persons familiar with them."
END OF WATT QUOTES FROM "MUHAMMAD IN MECCA" 
Those familiar with Watt's work know he is an excellent scholar, and that he bends over backward trying not to offend Muslim sensibilities. Here, Watt avoids taking the bull by the horns. Instead of addressing the question, "Did Muhammad have other sources (i.e. Judaism, Christianity, and paganism), which made up the Quran", Watt asks, "How did these religions influence the people and culture Muhammad grew up in? Finally, Watt does come out and implicitly say Muhammad was influenced by other religious stories because of the evidence in the Quran itself.
WATT, QUOTED FROM "MUHAMMAD IN MEDINA"
Watt again touches upon Muhammad's contact with Christians and Jews. He writes on page 315:
"There were a few Christians in Mecca, of whom one, Khadijah's cousin, Waraqah b. Nawfal, may have influenced Muhammad considerable; but the majority were probably Abyssinian slaves and not well instructed in the faith. Muhammad would also have seen something of Christianity while trading in Syria. Until he went to Medina he may have had practically no contacts with Jews.
And on page 320:
"One of the remarkable features of relationship between Muslims and Christians is that neither Muhammad nor any of the Companions seems to have been aware of some of the fundamental Christian doctrines. Apart from the reference to the crucifixion (which is primarily a denial of a Jewish claim), and the mention of the twelve apostles as the "helpers" of Jesus, and of miracles of healing and raising the dead, there is nothing in the Quran about the adult life and teaching of Jesus as recorded in the New Testament. The early Muslims gave Jesus the title of Messiah (Masih) but did not appreciate that it involved a claim to be "God's anointed". They did not understand the distinctive work of Jesus in redeeming the work and atoning for its sins. The did not realize that the Holy Spirit was regarded by Christians as the third person in the godhead. It is indeed remarkable that there should have been among the Muslims over such a wide area this absence of knowledge of Christianity. The blame for this state of affairs probably rests on those Christians with whom Muhammad and his Companions were in contact, who may themselves have had little appreciation of the doctrines mentioned. Nevertheless the "absence of knowledge remains, and in the thirteen centuries since Muhammad's time few Muslims have done anything to fill in the lacuna." 
Maxime Rodinson writes in "Muhammad", page 60:
"There can be no doubt that in Arabia, too, these events made a great impression. Among the Jews and the various Christian sects, propaganda was rife. The social conditions which favored its growth have already been described. Anyone in Mecca who was interested could easily find Jews and Christians who were only too ready to explain the basic tenets of their faith. In the case of the Christians it was unfortunate that they knew very little about their own religions. They were for the most part poor folk - traders, butchers, smiths, blood-cuppers, peddlers, wine-sellers, adventurers and slaves. They had no organized community, no priests or churches. They belonged to different sects, each convinced that the rest were heretics. 
Alfred Guillaume in "Islam", page 6, presents some historical background / contextual information regarding the sources Muhammad borrowed from
"his (Muhammad's) neighbors numbered many Jews; Christians were known to him from personal intercourse. In Mecca itself there was apparently no organized Christian community, though, as we shall see, there were large settlements of Christians with their own bishops, churches, and monasteries within easy reach of Mecca; indeed it would have been impossible to travel north, south, or east from Mecca without meeting with them."
And on page 11:
"There was a large Jewish colony in the Yaman (south of Mecca) in pre-Islamic times.....These Jews certainly go back to the fourth century A.D.....
At the dawn of Islam the Jews dominated the economic life of the Hijaz. They held all the best land in the oases of Taima, Fadak, and Wadi -l-Qura; at Medina they must have formed at least half of the population" 
H.A.R. Gibb in "Mohammedanism an Historical Survey" on pages 37, 38 writes regarding the sources of the Quran:
"Earlier scholars postulated a Jewish source with some Christian additions. More recent research has conclusively proved that the main external influences (including the Old Testament materials) can be traced back to Syriac Christianity.
It is now well known that there were organized Jewish and Christian churches amongst the settled communities in the north, the south, and the east of Arabia. The Arab town of Hira on the Euphrates was the seat of a Nestorian bishopric which almost certainly conducted some kind of missionary activity in Arabia, and there are many references in old Arabic poetry to hermits living in lonely cells in the wilderness. In the Yemen a Jewish or Judaizing movement supported by the local dynasty was overthrown by the Yemenite Christians with Abyssinian aid in A.D. 525. In view of the close commercial relations between Mecca and the Yemen it would be natural to assume that some religious ideas were carried to Mecca with the caravans of spices and woven stuffs, and there are details of vocabulary in the Koran which give color to this assumption."
Note here that Gibb points out that Christians could have taught Muhammad Old Testament stories as well as Christian stories. 
W. St. Clair Tisdall writes in "The Sources of Islam", on page 46, that,
"In the Prophet's day, numbers of Christians in Arabia were not only an ignorant people, but belonged to heretical Sects, which, on account of their dangerous influence, had been expelled from the Roman Empire and thus had taken refuge beyond the border land. They had hardly any acquaintance with the Gospel or Apostolic writings, but were conversant with heretical books and the extravagant tales they contained. Now our argument is that Mahomet having but an imperfect knowledge of the Gospel, leaned from these people who were all round him what he believed to be the purport of the New Testament. 
Tisdall also writes in "The Sources of the Quran", page 27, 28:
"To an intelligent mind the assertion (pure originality of the Quran) which we are considering refutes itself. Moreover, the morality of the Quran, its view of the Divine Nature, its anachronisms, and its many defects make it impossible for us to doubt that it s Muhammad's own composition. When the Surahs are arranged in the chronological order of their composition and compared with the events in Muhammad's life, we see that there is much truth in the statement that the passages were not as Muslims say, revealed, but composed from time to time, as occasion required, to sanction each new departure (from earlier moral positions) made by Muhammad. The Quran is a faithful mirror of the life and character of its author. It breathes the air of the desert, it enables us to hear the battle cries of the Prophet's followers as they rushed to the onset, it reveals the working of Muhammad's own mind, and shows the gradual declension of his character as he passed from the earnest and sincere though visionary enthusiast into the conscious impostor and open sensualist. All this is clear to every unprejudiced reader of the book."
. . . How much of the result [i.e. the Quran], is due to the character of Muhammad himself and to the circumstances of his time?" 
Finally, Charles Torrey in "The Jewish Foundation of Islam", writes on pages 42, 43:
"In two very important passages the Koran refers to human instruction received by the prophet, in both cases in answer to the caviling charge that his divine wisdom was only what might be acquired by any one who was willing to waste his time in listening to "old stories." The first of the passages is 25:5 f. "The unbelievers say: This is only falsehood of his own devising, and other people have helped him to it..... And they say: Old stories which he has written out for himself; and they are dictated to him morning and evening." This instruction given in Mekka, extending over some time. The stories from the Old Testament are especially referred to. Mohammed does not deny the human teacher, but only insists that the teaching came down from heaven. What the scoffing Mekkans said was certainly true as to the process by which the narrative material in the Koran was generally obtained. The teacher was some on whose continued intercourse with Mohammad they could observe, there in their own city. It was at home, not abroad, that the prophet received at least the Biblical (and Haggadic) narratives which occupy so large a part of the Koran.
And he writes on page 34:
"The Koran occasionally - and, be it noted, also in the Mekkan period - takes notice of the Jewish scholars (ahbar) the rabbis (rabbanis), the word denoting a still more learned class (Geiger, p. 52) as in 3:73 and 5:48, 68. In 26:197 Mohammed boasts that "the learned (ulema') of the children of Israel" had given him encouragement. This incidental testimony, supported as it is by the whole Koran, is certainly to be taken at its face value. To assert that there were no Israelite scholar in Mekka and Medina, and that Mohammed did not know the difference between the learned and the unlearned, is easy, but quite in disregard of the evidence. All the history of his dealing with "the people of the Book" - the amount of exact information, from Biblical and rabbinical sources, which he received; the encouragement given him while he seemed a harmless inquirer; the long and bitter argument, in which he was continually worsted; and the final rejection of all his prophetic claims - shows him in close contact with an old and perfectly assured religious tradition, far too strong for him. The history would have been the same if he had made his appearance, first as pupil and then as dangerous innovator, in any center of Israelite culture." 
I could continue to quote from other scholars, but the above is sufficient. And, in reading these quotes, a couple of things become obvious:
1) Their writings all agree that Muhammad learned via word of mouth. No one asserts that Muhammad read these other religious writings. That may have been a possibility, but because of the errors in the Quran, and the paucity of Quranic related material, it does not follow that Muhammad had substantial written material in front of him.
2) They also agree that various opportunities occurred in Muhammad's life for him to learn about the other religions. (Only a few of these events have been mentioned thus far.)
3) It wasn't necessary for these writings to be in Arabic. A Jew or Christian who knew the stories and speak Arabic could easily teach Muhammad the stories (as was the case in Mecca). Or a Christian slave from a Christian region could speak with Muhammad in Arabic and teach him his knowledge of Christianity, however imperfect it may have been. Even a pagan merchant could relate his knowledge. Muhammad, being generally ignorant of detailed Jewish and Christian teachings would be none the wiser.
4) None of these writers assert that there were "seats" of Judaism or Christianity located in the Hijaz. Of course there were Christians. And, yes, there were Jewish scholars. However, for Muhammad to learn about these religions, as imperfectly as he did, there need not be Ivy League seminaries available. All he needed was to speak to people barely knowledgeable of these religions.
Rev A: 9/12/99, Rev B: 9/21/01