That the knowledge which finds its way into the hearts of the prophets comes from the angels
One way to make this clear is to say: The definite kinds of knowledge that enter the hearts of the prophets—and of other human beings—must either have a cause that brings them about, or they must arise without any cause whatsoever, as some theologians of kalām who deny causality in existence claim. If there is no cause, their assertion that such knowledge issues from the intellect or from the soul collapses. If, however, there is a cause, it could perfectly well be angels who convey that knowledge, or jinn who instruct certain people; and the philosophers have absolutely no proof for dismissing this, even on their own premises—whether they speak of the eternity of the aflāk (celestial spheres) and their emanation from a cause that necessarily accompanies them, as Ibn Sīnā maintains, or claim, with Aristotle and his followers, that the cause merely sets them in motion as a model moves one who imitates it. On either view, reason offers no argument that rules out angelic agency. Since that possibility stands, their position is refuted. Indeed, we contend that whenever such knowledge does have a cause, that cause must be the angels; for the idea that it proceeds from the celestial soul has been shown false, and so the only remaining alternative is that it comes from the angels—and that is precisely what we sought to establish.

A number of Muslim dialecticians and philosophers have confirmed the existence of angels and jinn by this very route. They say: we experience, without any deliberate intention on our part, certain occurrences within our souls—acts of knowing and willing, as well as thoughts akin to them, whether doubts or cravings. All of these must have an agent who brings them into our hearts. God, exalted be He, is the Creator of everything, yet He creates nothing without a cause, as an inductive examination of His creation shows; no event occurs except through a preceding event. A person may find his heart free of belief in either of two opposites, and free of inclination toward either; then suddenly one of the two lodges itself in his heart. That necessarily requires a new cause to account for it. It is inadmissible to attribute this merely to the celestial movements, for on any given day the relation of those movements to all individuals is identical, while people differ in these inner promptings to an indescribable degree. Even one and the same person differs with himself: at one time he is a believer, at another an unbeliever, at yet another devoutly righteous…