Christoph Luxenberg, a scholar of ancient Semitic languages in Germany, argues that the Koran has been misread and mistranslated for centuries. His work, based on the earliest copies of the Koran, maintains that parts of Islam's holy book are derived from pre-existing Christian Aramaic texts that were misinterpreted by later Islamic scholars who prepared the editions of the Koran commonly read today.
So, for example, the virgins who are supposedly awaiting good Islamic martyrs as their reward in paradise are in reality "white raisins" of crystal clarity rather than fair maidens.
http://www.corkscrew-balloon.com/02/03/1bkk/04b.html
Not to mention that the Koran was written over 100 years after Mohammad's death and that there were no persons alive who heard anything he said first hand.