The Qur'an, the main holy book of Islam, had a significant influence on the Arab language, and marked the beginning of Islamic literature. It was transcribed in the Arabic dialect of the Quraysh, the tribe of Muhammad. As Islam spread, the Quran had the effect of unifying and standardizing Arabic. Not only is the Qur'an the first work of any significant length written in the language, but it also has a far more complicated structure than the earlier literary works with its 114 "suras" (chapters) which contain 6,236 "ayat" (verses). It contains injunctions, narratives, homilies, parables, direct addresses from God, instructions and even comments on itself on how it will be received and understood. It is also admired for its layers of metaphor as well as its clarity, a feature it mentions itself in sura 16:103. The 92 Meccan suras, believed to have been revealed to Muhammad in Mecca before the Hijra, deal primarily with , or "the principles of religion," whereas the 22 Medinan suras, believed to have been revealed to him after the Hijra, deal primarily with Sharia and prescriptions of Islamic life. The word Qur'an meant "recitation", and in early times the text was transmitted orally. The various tablets and scraps on which its suras were written were compiled under Abu Bakr (573-634), and first transcribed in unified "masahif", or copies of the Qur'an, under Uthman (576-656). Although it contains elements of both prose and poetry, and therefore is closest to "Saj" or rhymed prose, the Qur'an is regarded as entirely apart from these classifications. The text is believed to be divine revelation and is seen by Muslims as being eternal or 'uncreated'. This leads to the doctrine of "i'jaz" or inimitability of the Qur'an which implies that nobody can copy the work's style. This doctrine of i'jaz possibly had a slight limiting effect on Arabic literature; proscribing exactly what could be written. Whilst Islam allows Muslims to write, read and recite poetry, the Qur'an states in the 26th sura (Ash-Shu'ara or The Poets) that poetry which is blasphemous, obscene, praiseworthy of sinful acts or attempts to challenge the Qu'ran's content and form is forbidden for Muslims. This may have exerted dominance over the pre-Islamic poets of the 6th century whose popularity may have vied with the Qur'an amongst the people.