Numbers 31:21-24

21Eleazar the priest said to the soldiers, ‘This is the rule that the Lord told Moses:

22You must put all the gold, the silver, the bronze, the iron, and other metals in a fire.

23Put in the fire anything that the fire will not destroy. The fire will make those things clean. But you must also wash them with water. As for anything that the fire would destroy, wash them with water to make them clean.

24On the seventh day, you must wash your clothes. After that you will be clean again. Then you can come into the camp.’