Muhammad's inspirations. However, Muhammad's critics accused him of being a possessed man, a soothsayer or a magician since his experiences were similar to those claimed by such figures well known in ancient Arabia. Welch additionally states that it remains uncertain whether these experiences occurred before or after Muhammad's initial claim of prophethood. The Quran describes Muhammad as "," which is traditionally interpreted as 'illiterate', but the meaning is rather more complex. Medieval commentators such as Al-Tabari maintained that the term induced two meanings: first, the inability to read or write in general; second, the inexperience or ignorance of the previous books or scriptures (but they gave priority to the first meaning). Muhammad's illiteracy was taken as a sign of the genuineness of his prophethood. For example, according to Fakhr al-Din al-Razi, if Muhammad had mastered writing and reading he possibly would have been suspected of having studied the books of the ancestors. Some scholars such as Watt prefer the second meaning of —they take it to indicate unfamiliarity with earlier sacred texts. The final verse of the Quran was revealed on the 18th of the Islamic month of Dhu al-Hijjah in the year 10 A.H., a date that roughly corresponds to February or March 632. The verse was revealed after the Prophet finished delivering his sermon at Ghadir Khumm. Compilation and preservation Following Muhammad's death in 632, a number of his companions who knew the Quran by heart were killed in the Battle of Yamama by Musaylimah. The first caliph, Abu Bakr (d. 634), subsequently decided to collect the book in one volume so that it could be preserved. Zayd ibn Thabit (d. 655) was the person to collect the Quran since "he used to write the Divine Inspiration for Allah's Apostle". Thus, a group of scribes, most importantly Zayd, collected the verses and produced a hand-written manuscript of the complete book. The manuscript according to Zayd remained with Abu Bakr until he died. Zayd's reaction to the task and the difficulties in collecting the Quranic material from parchments, palm-leaf stalks, thin stones (collectively known as ) and from men who knew it by heart is recorded in earlier narratives. In 644, Muhammad's widow Hafsa bint Umar was entrusted with the manuscript until the third caliph, Uthman ibn Affan, requested the standard copy from her. In about 650, Uthman (d. 656) began noticing slight differences in pronunciation of the Quran