Muhammad's clouded crystal ball

Since Rambo referred to the argument from prophecy to vindicate the inspiration of Muhammad, it is worth noting that Koranic prophecies have not gone unchallenged.

http://answering-islam.org/Shamoun/false_prophecies.htm

By the same author is a discussion of Koranic textual criticism:

http://answering-islam.org/Shamoun/quran_variants.htm