Numbers 31:17-19

New International Version - UK

¹⁷ Now kill all the boys. And kill every woman who has slept with a man, ¹⁸ but save for yourselves every girl who has never slept with a man.

¹⁹ ‘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.