Ibn warraq says that the historicity of Muhammad is doubtful :
- Although the unreliability of the Arabic literary sources has been known for a century, only recently have scholars begun to explore its full implications, thanks largely to the ground-breaking work of the American scholar John Wansbrough.
- Philologists and scholars look skeptically at the Arabic written sources and conclude that these are a form of "salvation history" - self-serving, unreliable accounts by the faithful.
- Most of the material asserted by Islamic revisionist scholars is dubious, written mostly to promote of a self serving religious agenda. The use of the historical methods disproves most of the traditional accounts to such a degree that Patricia Crone has written, that "one could, were one so inclined, rewrite most of Montgomery Watt's biography of Muhammad in reverse." For example, an inscription and a Greek account leads Lawrence Conrad to fix Muhammad's birth in 552, not 570.
- Patricia Crone contends that the events of Muhammad's life did not take place in Mecca as believed by traditionalists but hundreds of miles to the north.
- Yehuda D. Nevo and Judith Koren trace the origins of classical Arabic to the Levant rather than in what is today Saudi Arabia and that it only spread to Arabia through the military expansions of one of the early caliphs.
- The Arab tribes who conquered great expanses of land in the seventh century were not Muslims, but pagans.
- The Qu'ran is actually a collection of adaptations from earlier Judeo-Christian liturgical materials compiled by self-serving later authors.
- Islam did not come into existence until two or three hundred years after the date claimed by traditional Muslim accounts (around CE 830).
- Islam developed not in the far deserts of Arabia but through the interaction of Arab conquerors with the societies they overran.
- Quest for the Historical Muhammad raises basic questions for Moslems concerning the prophet's role as a moral paragon; the sources of Islamic law; and the God-given nature of the Koran.
For more details You can go buy the book The Quest for the Historical Muhammad by Ibn Warraq at your library. Plus there are many mistakes in the quran i.e grammatical, spelling, structure and contradictions in it. And I forgot to mention that there were 17 different versions of the koran everyone had each in different languages one in Syriac, Aromic , Arabic , and Persian. Each of his companions 4 korans.Remember the historicity of islam is still doubtful. After that Othman Bin Affan burned all of the korans and left Omar's version which we have now and muslims follow.