Números 31:19

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.

19 You yourselves will have to keep outside the tent-circle for seven days, anyone of you who has put any person to death or come near a dead body; and on the third day and on the seventh day make yourselves and your prisoners clean.