قل لو شاء الله ما تلوته عليكم ولا أدراكم به فقد لبثت (10:16) بالانجليزي

(10:16) Tell them: 'Had Allah so willed, I would not have recited the Qur'an to you, nor would Allah have informed you of it. I have spent a lifetime among you before this. Do you, then, not use your reason? *21

Tafseer Abu-al-A'la Maududi

Page 210 English Traditional

*21). This is indeed a very weighty argument in refutation of the unbelievers' allegation that the Prophet (peace be on him) had himself authored the Qur'an and subsequently ascribed it to God. So far as other arguments are concerned, they might be considered as somewhat remote. But the argument based on the life and character of the Prophet (peace be on him) was particularly weighty since the Makkans were thoroughly familiar with the whole of his life. Before his designation as a Prophet, he had spent a full forty years in their midst. He was born in their city. They had observed his childhood, and then his youth, and it was in their city that he had reached his middle age. He had also had a variety of dealings with them. He had had social interaction, business transactions, matrimonial ties, and relationships of every conceivable nature with his people so that no aspect of his life was hidden from their view. Could there be a more powerful testimony to the truth of his claim to prophethood than his blameless life and character?
Two things about the life of the Prophet (peace be on him) were especially clear and were quite well known to all Makkans. First, that during the forty years of his life before his designation as a Prophet, he had received no instruction from, or even enjoyed the company of learned people which could have served as the source of the ideas which began to flow, as would a stream, from his lips as soon as he claimed, at the age of forty, that he had been designated as a Prophet. Before that he was never seen to have been concerned with the problems, or to have discussed the subjects, or to have expressed the ideas which frequently recur in the Qur'an. In fact none of his closest friends and relatives had foreseen in his pre-Prophetic life any signs indicative of the great message which he suddenly started to preach at the age of forty. These pieces of evidence, taken together, provide incontrovertible evidence that the Qur'an is not a product of the Prophet's mind; that it had come to the Prophet (peace be on him) from without. For no human being can produce something for which traces of growth and evolution are not found in the earlier period of his life.
This explains the fact that when some of the more crafty Makkan unbelievers realized the sheer absurdity of their allegation that the Prophet (peace be on him) was the author of the Qur'an, they chose to propagate that there must be some other person who had taught the Prophet (peace be on him) the Qur'an. Such a statement, however, was even more preposterous since they failed to convincingly point out who that other person was who was the true source of the Qur'an. Even leaving aside Makka, the fact is that there was not a single person throughout the length and breadth of Arabia who possessed the competence needed for the authorship of the Qur'an. Had such an extraordinary person existed, how could he have remained hidden from the sight of others?
Second, the pre-Prophetic life of Muhammad (peace be on him) clearly shows him to be a man of exceptionally high moral character for there was not the least trace of any evil - whether lies, deceit, vile cunning or trickery. On the contrary, all those who came into contact with the Prophet (peace be on him) were impressed by him as a person of flawless character, as one utterly truthful and trustworthy.
An illustration in point is the incident related in connection with the re-building of the Ka'bah five years before his designation as a Prophet. There was a serious dispute between the various families of the Quraysh on the question as to who should have the privilege of placing the Black Stone in its place in the edifice of the Ka'bah, In order to reach an amicable accord, they resolved that they would abide by the ruling given by the first person who entered the Ka'bah the following day. The next day people saw it was the Prophet (peace be on him) who was the first to enter. They exclaimed: 'Here is a trustworthy man (amin). We agree [to follow his ruling]. He is Muhammad.' (Ibn Sa'd, al-Tabaqat, vol. 1, p. 146 - Ed.) Thus, before designating
Muhammad (peace be on him) as a Prophet, God had the whole body of the Quraysh testify to his trustworthiness. No room was left, therefore, for suspecting that he who had never resorted to lying or deceit throughout his life would suddenly resort to fabricating a gigantic lie; that he would first compose something, then deny that it was his work, and would then ascribe it to God.
In view of the above, God directs the Prophet (peace be on him) to ask the unbelievers to use their brains before levelling such a stupid allegation against him. For the Prophet (peace be on him) was after all no stranger to them; he had spent virtually a whole lifetime in their midst. In view of the well-known and uniformly high level of his conduct and character, how could it even be conceived that he would falsely ascribe the Qur'an to God if God had not actually revealed it to him. (For further elaboration see al-Qasas 28, n. 109.)