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 text 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. According to Shia, Ali ibn Abi Talib (d. 661) compiled a complete version of the Quran shortly after Muhammad's death. The order of this text differed from that gathered later during Uthman's era in that this version had been collected in chronological order. Despite this, he made no objection against the standardized Quran and accepted the Quran in circulation. Other personal copies of the Quran might have existed including Ibn Mas'ud's and Ubay ibn Ka'b's codex, none of which exist today. The Quran most likely existed in scattered written form during Muhammad's lifetime. Several sources indicate that during Muhammad's lifetime a large number of his companions had memorized the revelations. Early commentaries and Islamic historical sources support the above-mentioned understanding of the Quran's early development. University of Chicago professor Fred Donner states that:[T]here was a very early attempt to establish a uniform consonantal text of the Qurʾān from what was probably a wider and more varied group of related texts in early transmission.… After the creation of this standardized canonical text, earlier authoritative texts were suppressed, and all extant manuscripts—despite their numerous variants—seem to date to a time after this standard consonantal text was established.Although most variant readings of the text of the Quran have ceased to be transmitted, some still are. There has been no critical text produced on which a scholarly reconstruction of the Quranic text could be based. Historically, controversy over the Quran's content has rarely become an issue, although debates continue on the subject. In 1972, in a mosque in the city of Sana'a, Yemen, manuscripts were discovered that were later proved to be the most ancient Quranic text known to exist at the time. The Sana'a manuscripts contain palimpsests, a manuscript page from which the text has been