Tafsir of Al-A'raf 7:120

This took place in the definite presence of Pharaoh. It is permitted that the pronoun in "they were overcome" and "they returned" refers to the magicians as well; however, this is contested on the basis that they [the magicians] were not in a state of humiliation [before their conversion]. Interpreting it as fear of Pharaoh or as a state prior to their faith involves difficulties that are not hidden.

The intended meaning of "the magicians fell down" is that they collapsed into prostration. This expression is used—rather than simply saying "they prostrated"—to draw attention to the fact that the Truth dazzled them and compelled them to prostrate in such a way that they lost all self-control; it is as if someone pushed them and cast them down. Alternatively, it signifies that Allah the Exalted inspired them to do so and compelled them toward it; thus, the "caster" is Allah, through His inspiration to them, so that Pharaoh might be broken by the very people he intended to use to break Moses (peace be upon him), turning the matter back upon him. It is also possible that the phrasing serves as a metaphor to emphasize the speed and intensity of their falling down, to which the words of al-Akhfash point. It is also permitted that this expression is used as a formal correspondence (mushakala) to the "casting" mentioned previously [the casting of the ropes and staffs], though this is less significant than what preceded it.

It is narrated that the gathering of the people took place in Alexandria, that the tail of the serpent reached beyond the sea, and that it opened its mouth eighty cubits wide, swallowing what they had crafted one after another, then headed toward the people. The people panicked, a stampede ensued, and twenty-five thousand of them died because of it. Then Moses (peace be upon him) took it, and it returned in his hand to being a staff as it was before. Allah the Exalted, by His power, annihilated those massive bodies, or it is possible that He, Glory be to Him, dispersed them into subtle particles. When the magicians saw this, they knew it was a matter from Heaven and nothing of sorcery at all; thereupon, they fell down prostrating.

The immediate understanding of "prostration" is its literal meaning, and it is not unlikely that they were familiar with its manner. It is said that Moses and Aaron (peace be upon them) prostrated in gratitude to Allah the Exalted for the manifestation of the Truth, and the magicians followed their lead and prostrated with them. To interpret "prostration" here as mere "submission"—that is, that they yielded due to what they saw—is contrary to the apparent meaning indicated by the traditions, with no compelling reason to adopt such an interpretation.