Numbers 31:19-24

19And encamp ye without the camp seven days: whosoever hath killed any person, and whosoever hath touched any slain, purify yourselves on the third day and on the seventh day, ye and your captives.

20And as to every garment, and all that is made of skin, and all work of goats’ hair, and all things made of wood, ye shall purify yourselves.

21And Eleazar the priest said unto the men of war which went to the battle, This is the statute of the law which the LORD hath commanded Moses:

22howbeit the gold, and the silver, the brass, the iron, the tin, and the lead,

23every thing that may abide the fire, ye shall make to go through the fire, and it shall be clean; nevertheless it shall be purified with the water of separation: and all that abideth not the fire ye shall make to go through the water.

24And ye shall wash your clothes on the seventh day, and ye shall be clean, and afterward ye shall come into the camp.