What About Salman - The Persian?
Menezes[1] and Gardner[2], postulated a completely different teacher for the Prophet(P). They maintained that Salmân, a Persian, had helped in writing the sacred Book. It was one of the suggestions of Tisdall[3] too. Salmân, who had been a Zoroastrian before accepting Christianity in Syria, later moved on to Medina where he met the Prophet(P) and accepted Islam. Salmân's life is documented in Islamic history, notably as the very first person to propose digging a trench for the defense of Medina when the city was threatened with invasion by the Meccan disbelievers and their allies. His bright suggestion, coupled with violent wintry gales, successfully repelled the enemy.
It is well known to Muslims that the greater part of the Qur'ân, i.e., about two thirds of it, was revealed in Mecca before the Prophet(P) migrated to Medina (this includes the stories of Biblical Prophets!), where Salmân met him. Furthermore, the Book's literary style is so sublime that even born Arab linguists who have tried over the years to imitate it have not been successful - to say nothing of a Persian.
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References
[1] F. J. L. Menezes, The Life & Religion Of Muhammad, The Prophet Of Arabia, 1911, Sands, London, p.161.
[2] J. Gardner, Faiths Of The World, 1920, Volume 2, Fullerton, p.279.
[3] Rev. W. St. Clair Tisdall, The Original Sources Of The Qur'an, 1905, Society For The Promotion Of Christian Knowledge, London, p.134.
Khâlid al-Khazrâjî, Mustafa Ahmed, Elias Karîm, Qasim Iqbal, cAbd ar-Rahmân Robert Squires, M S M Saifullah & Muhammad Ghoniem