John Calvin Commentary Numbers 16:15

"And Moses was very wroth, and said unto Jehovah, Respect not thou their offering: I have not taken one ass from them, neither have I hurt one of them." — Numbers 16:15 (ASV)

And Moses was very wroth. Although it might be that there was something of human passion here, still zeal for God was supreme in his mind, nor did intemperate feelings, if he was at all tempted by them, prevail. Assuredly, it appears probable from the context that he was inflamed with holy ardor, since he executes the vengeance of God as His lawful minister, so that it is clear he neither spoke nor did anything but at the dictation of the Spirit. Indeed, we shall soon see that, although he was anxious regarding the public safety, he required that only a few offenders should be punished, and not that the multitude should perish.

Nor does his anger burst forth into abusive language, as those who are carried away by excess usually assail the enemies by whom they are injured with their tongue as well as their hands; instead, he turns to God. Nor does he ask for more than that they may be brought to shame in their pride. This is, indeed, generally expounded by many as if Moses desired that God should have no mercy upon them. But inasmuch as the decision of the quarrel depended on the approval or rejection by God of the offering they were about to make, he does not seem to me to pray for more than that God, by refusing their polluted gift, should thus chastise their ambition.

At the same time, he also shows that his prayer springs from the confidence of a good conscience, when he dares to testify before God that he had injured no one. Now this was the height of integrity and disinterestedness, that when the people owed everything to him, he had not taken even the value of a single ass as the reward of all his labors.