It is important that we take a close look at the Quran, the inviolable, immutable charter of Islam, since it enjoys such a sanctified standing. Muslims believe that the Quran is written by Allah himself. Allah handed down the book, piece by piece and chapter by chapter, to the Archangel Gabriel. Gabriel, in turn, whispered these words to Muhammad himself over the course of some 23 years.
Muhammad could neither read nor write. Therefore, he had to find people who could write down what he called his revelations from Allah. There were several of these katibs (scribes) who wrote down the surahs (chapters) which eventually made up the Quran.
There are several problems with the Quran. A few will be listed here.