Numbers 31:19-24

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

20You shall purify every garment, every article of skin, all work of goats' hair, and every article of wood."

21Then Eleazar the priest said to the men in the army who had gone to battle: "This is the statute of the law that the Lord has commanded Moses:

22only the gold, the silver, the bronze, the iron, the tin, and the lead,

23everything that can stand the fire, you shall pass through the fire, and it shall be clean. Nevertheless, it shall also be purified with the water for impurity. And whatever cannot stand the fire, you shall pass through the water.

24You must wash your clothes on the seventh day, and you shall be clean. And afterward you may come into the camp."