Numbers 31:17-19

Young's Literal Translation

¹⁷ `And now, slay ye every male among the infants, yea, every woman known of man by the lying of a male ye have slain;

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;