Ali ibn Sahl Rabban al-Tabari

"When I was a Christian I used to say, as did an uncle of mine who was one of the learned and eloquent men, that eloquence is not one of the signs of prophethood because it is common to all the peoples; but when I discarded (blind) imitation and (old) customs and gave up adhering to (mere) habit and training and reflected upon the meanings of the Quran I came to know that what the followers of the Quran claimed for it was true. The fact is that I have not found any book, be it by an Arab or a Persian, an Indian or a Greek, right from the beginning of the world up to now, which contains at the same time praises of God, belief in the prophets and apostles, exhortations to good, everlasting deeds, command to do good and prohibition against doing evil, inspiration to the desire of paradise and to avoidance of hell-fire as this Quran does. So when a person brings to us a book of such qualities, which inspires such reverence and sweetness in the hearts and which has achieved such an everlasting success and he is (at the same time) an illiterate person who did never learnt the art of writing or rhetoric, that book is without any doubt one of the signs of his Prophet-hood."