Deuteronomy 20:12-14

12And if it will make no peace with thee, but will make war against thee, then thou shalt besiege it:

13and when the LORD thy God delivereth it into thine hand, thou shalt smite every male thereof with the edge of the sword:

14but the women, and the little ones, and the cattle, and all that is in the city, even all the spoil thereof, shalt thou take for a prey unto thyself; and thou shalt eat the spoil of thine enemies, which the LORD thy God hath given thee.