John Gill Commentary Numbers 31:15

"And Moses said unto them, Have ye saved all the women alive?" — Numbers 31:15 (ASV)

And Moses said to them, have you saved all the women alive ?

] Which either had been reported to him, or he concluded, by seeing so many with them; and this question is put, not for information, but by way of reproof, and as chiding them for what they had done; for they might have received orders from him to put them to death, when he sent them out; and if so, there was the more reason to be angry with them; or he might conclude they would have done this of themselves, knowing what instruments of mischief these women had been to Israel.