Numbers 31:19-24

19And encamp outside the camp seven days; whoever hath killed a person, and whoever hath touched any slain; ye shall purify yourselves on the third day, and on the seventh day, you and your captives.

20And every garment, and every vessel of skin, and all work of goat's hair, and every utensil of wood shall ye purify.

21And Eleazar the priest said to the men of war that had gone to the battle, This is the statute of the law which Jehovah hath commanded Moses.

22Only the gold, and the silver, the copper, the iron, the tin, and the lead,

23everything that passeth through the fire, ye shall make it go through the fire, and it shall be clean; only it shall be purified with the water of separation; and everything that cannot pass through the fire ye shall make go through the water.

24And ye shall wash your garments on the seventh day, and ye shall be clean; and afterwards ye may come into the camp.