Numbers 31:21-23

Then Eleazar the priest said to the men of war who had been to the fight, This is the rule of the law which the Lord has given to Moses: But gold and silver and brass and iron and tin and lead, And anything which may be heated, is to go through the fire and be made clean; but in addition it is to be put in the water of cleaning: and anything which may not go through the fire is to be put in the water.