Numbers 31:18-20

Young's Literal Translation

¹⁸ and all the infants among the women, who have not known the lying of a male, ye have kept alive for yourselves.

¹⁹ `And ye, encamp ye at the outside of the camp seven days -- any who hath slain a person, and any who hath come against a pierced one, ye cleanse yourselves on the third day, and on the seventh day -- ye and your captives;

²⁰ and every garment, and every skin vessel, and every work of goats' [hair], and every wooden vessel, ye yourselves cleanse.'