Numbers 19:18

19:18 Then a ceremonially clean person must take hyssop, dip it in the water, and sprinkle it on the tent, on all its furnishings, and on the people who were there, or on the one who touched a bone, or one killed, or one who died, or a grave.

Numbers 31:8

31:8 They killed the kings of Midian in addition to those slain – Evi, Rekem, Zur, Hur, and Reba – five Midianite kings. They also killed Balaam son of Beor with the sword.

Numbers 31:19

Purification After Battle

31:19 “Any of you who has killed anyone or touched any of the dead, remain outside the camp for seven days; purify yourselves and your captives on the third day, and on the seventh day.