Jamieson, Fausset and Brown on Numbers 16:4

4. when Moses heard it, he fell upon his face--This attitude of prostration indicated not only his humble and earnest desire that God would interpose to free him from the false and odious imputation, but also his strong sense of the daring sin involved in this proceeding. Whatever feelings may be entertained respecting Aaron, who had formerly headed a sedition himself [Nu 12:1], it is impossible not to sympathize with Moses in this difficult emergency. But he was a devout man, and the prudential course he adopted was probably the dictate of that heavenly wisdom with which, in answer to his prayers, he was endowed.