NUM 31:19

19 and dwell ye without the tents seven days. He that slayeth a man, or toucheth a slain man, shall be cleansed in the third [[day]], and the seventh day; (and then stay ye away from the tents for seven days. He who killeth a man, or toucheth a dead man, must cleanse both himself, and his captives, on the third day, and on the seventh day;)