Numbers 31:21-23

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.