Muslims believe the Koran is not only perfect, but that it's uncreated. What's that mean? The Koran says that Allah has in his possession the "Mother of the Book" (13:39). And Allah made the Koran "in Arabic, that ye may be able to understand" (43:3) and tells Muhammad that "it is in the Mother of the Book, in Our Presence" (43:4). The "Mother of the Book" is, according to Islamic tradition, the Preserved Tablet, the copy of the Koran that has existed for all eternity with Allah (85:21-22). (pp. 25-26)One wonders, then, how it is that changes could have been introduced in the text.
Muhammad received Koranic revelations from Gabriel piecemeal-or, as the Koran itself says, "in slow, well-arranged stages, gradually" (25:32) - for twenty-three years. But Muhammad himself was "unlettered" 97:157), and did not write down his revelations. Before he died rather suddenly in 632, he had a premonition of his death - a premonition that was connected to the text of the Koran: "Every year," he told his daughter Fatima, "Gabriel used to revise the Qu'ran with me once only, but this year he has done so twice. I think this portends my death."
Nevertheless, Muhammad didn't make any provisions to pass on the complete Koranic text to his followers. Some of the Koran had been written down; other portions were preserved only in the memories of various Muslims. Accordingly, some revelations were forgotten, as the Koran itself acknowledges: "None of Our revelations do We abrogate or cause to be forgotten, but We substitute something better or similar" (2:106) (pp. 28-29)