Numbers 31:21-24

And Eleazar the priest said unto the men of war which went to the battle, This is the ordinance of the law which the LORD commanded Moses; only the gold, and the silver, the brass, the iron, the tin, and the lead, every thing that may abide the fire, ye shall make it 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 go through the water. And ye shall wash your clothes on the seventh day, and ye shall be clean, and afterward ye shall come into the camp.