Numbers 31:14-18

14But Moses was angry with the officers of the army, the commanders of thousands and of hundreds, who served in the war.

15And Moses said to them, “Have you let all the women live?

16Look, these [are the women who] caused the Israelites, by the counsel of Balaam, to trespass against the Lord in the matter of Peor, and so a plague came among the congregation of the Lord.

17Now therefore, kill every male among the children, and kill every woman who is not a virgin.

18But all the young girls who have not known a man intimately, keep alive for yourselves [to marry].