Numbers 31:15-18

15And Moses said unto them, Have ye saved all the women alive? 16Behold, these caused the children of Israel, through the counsel of Balaam, to commit trespass against Jehovah in the matter of Peor, and so the plague was among the congregation of Jehovah. 17Now therefore kill every male among the little ones, and kill every woman that hath known man by lying with him. 18But all the women-children, that have not known man by lying with him, keep alive for yourselves.