The Qur’an, (Koran) meaning recitation, is the sacred book of Islam. According to Muslim tradition, it was revealed by God to the Prophet Muhammad in separate revelations over the major portion of his life at Mecca and at Medina. The Qur'an was probably compiled as a single volume under the third caliph, Uthman, who appointed a committee (651-52). The internal organization of the Qur'an is somewhat ad hoc.