In about 650, the third Caliph Uthman ibn Affan (d. 656) began noticing slight differences in pronunciation of the Quran as Islam expanded beyond the Arabian Peninsula into Persia, the Levant, and North Africa. In order to preserve the sanctity of the text, he ordered a committee headed by Zayd to use Abu Bakr's copy and prepare a standard copy of the Quran. Thus, within 20 years of Muhammad's death, the Quran was committed to written form. That text became the model from which copies were made and promulgated throughout the urban centers of the Muslim world, and other versions are believed to have been destroyed. The present form of the Quran text is accepted by Muslim scholars to be the original version compiled by Abu Bakr.