Origins of Qu'ran

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Some non-muslim scholars accept a similar account, but without accepting any supernatural claims: they say that Muhammad put forth verses and laws that he claimed to be of divine origin; that his followers memorized or wrote down his revelations; that numerous versions of these revelations circulated after his death in 632 CE. They claim that first Abu Bakr ordered its compilation and then Uthman ordered the collection and ordering of this mass of material circa 650-656. These scholars point to many attributes of the Qur'ān as indicative of a human collection process that was extremely respectful of a miscellaneous collection of original texts. [33]
Other scholars have proposed that some development of the text of the Qur'ān took place after the death of Muhammad and before the currently accepted version of the Qur'ān stabilized. Western academic scholars associated with such theories include John Wansbrough, Patricia Crone, Michael Cook, Christoph Luxenberg, and Gerd R. Puin. They claim support from text within the oldest Qur'an; which is Qur'an in the House of Manuscript in Sana'a.
Another scholar, James A. Bellamy, has proposed some emendations to the text of the Qur'ān.
Other non-muslim translaters mean, that not only the Bible and Torah are sources of the Quoran but also Arabic mythology, like the mythes about Alexander the Great who should be called Zul-qurnain in verse 18.86.

18.86. Until, when he reached the setting of the sun, he found it set in a spring of murky water: Near it he found a People: We said: "O Zul-qarnain! (thou hast authority,) either to punish them, or to treat them with kindness."

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Arabic even has a name for persons who memorize the Qu'ran perfectly.

A hafiz is who memorizes and Tajweed is the word of perfect memory.