Numbers 31:17 WEB

¹⁵  Moses said to them, Have you saved all the women alive?

¹⁶  Behold, these caused the children of Israel, through the counsel of Balaam, to commit trespass against Yahweh in the matter of Peor, and so the plague was among the congregation of Yahweh.

¹⁷  Now therefore kill every male among the little ones, and kill every woman who has known man by lying with him.

¹⁸  But all the girls, who have not known man by lying with him, keep alive for yourselves.

¹⁹  Encamp you outside of the camp seven days: whoever has killed any person, and whoever has touched any slain, purify yourselves on the third day and on the seventh day, you and your captives.