he falls before his forehead has yet followed his chin downward; for that reason the verse says,

“upon their chins.”

It is also possible that the intended sense is “they fall upon their faces,” with the chin mentioned as a pars pro toto, just as a part can stand for the whole or a particular for the general.

I say: the one who falls on his chin does not prostrate on the chin, for the chin is not among the limbs of prostration. The limbs of prostration are seven, as the Prophet—may Allah bless him and grant him peace—said:

“I have been commanded to prostrate on seven limbs: the forehead”—and he pointed to his nose—“the two hands, the two knees, and the two feet.”

Were he to prostrate on his chin