Numbers 31:19-20

Abide without the camp seven days According to the law, Leviticus 15:13. Purify yourselves With the water of sprinkling, Numbers 19:9. Your raiment Namely, your spoil and prey. All work All which had contracted some ceremonial uncleanness, either from the dead bodies which wore them, or the tents or houses where they were, in which such dead bodies lay, or from the touch of the Israelitish soldiers, who were legally defiled by the slaughters they made.