Numbers 31:17-24

Now kill all the boys. And kill every woman who has slept with a man, but save for yourselves every girl who has never slept with a man. “Anyone who has killed someone or touched someone who was killed must stay outside the camp seven days. On the third and seventh days you must purify yourselves and your captives. Purify every garment as well as everything made of leather, goat hair or wood.” Then Eleazar the priest said to the soldiers who had gone into battle, “This is what is required by the law that the LORD gave Moses: Gold, silver, bronze, iron, tin, lead and anything else that can withstand fire must be put through the fire, and then it will be clean. But it must also be purified with the water of cleansing. And whatever cannot withstand fire must be put through that water. On the seventh day wash your clothes and you will be clean. Then you may come into the camp.”