Numbers 31:19-24

191And you, camp outside the camp seven days; whoever has killed any person and whoever has touched any slain, purify yourselves, you and your captives, on the third day and on the seventh day. 20You shall purify for yourselves every garment and every article of 2leather and all the work of goats’ hair, and all articles of wood.”

21Then Eleazar the priest said to the men of war who had gone to battle, “This is the statute of the law which the Lord has commanded Moses: 22only the gold and 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, but it shall be purified with 3water for impurity. But whatever cannot stand the fire you shall pass through the water. 24And you shall wash your clothes on the seventh day and be clean, and afterward you may enter the camp.”