“When was the Koran written? It existed first in oral form as series of revelations recited by the prophet Muhammad (570-632), founder of Islam. His followers wrote down or committed to memory the individual surahs, or chapters, but these were not collected in authoritative form until about 650.”
Excerpted from: Corey, Melinda, and George Ochoa. Literature: The New York Public Library Book of Answers. New York: Simon and Schuster, 1993.