Numbers 31:19-24

19Moses said, ‘Any soldier who has killed someone, or who has touched a dead body is unclean. He must stay outside the camp for seven days. On the third day and on the seventh day, you must wash yourselves to become clean. You must do the same thing to your Midianite prisoners.

20You must also make these things clean: any clothes or anything made from leather, wool or wood.’

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.’