Numbers 31:17-24

So kill all the boys and all the women who have had intercourse with a man. Only the young girls who are virgins may live; you may keep them for yourselves. And all of you who have killed anyone or touched a dead body must stay outside the camp for seven days. You must purify yourselves and your captives on the third and seventh days. Purify all your clothing, too, and everything made of leather, goat hair, or wood.” Then Eleazar the priest said to the men who were in the battle, “The LORD has given Moses this legal requirement: Anything made of gold, silver, bronze, iron, tin, or lead— that is, all metals that do not burn—must be passed through fire in order to be made ceremonially pure. These metal objects must then be further purified with the water of purification. But everything that burns must be purified by the water alone. On the seventh day you must wash your clothes and be purified. Then you may return to the camp.”