Numbers 19:18-19

18Then someone who is ceremonially clean must take a hyssop branch and dip it into the water. That person must sprinkle the water on the tent, on all the furnishings in the tent, and on the people who were in the tent; also on the person who touched a human bone, or touched someone who was killed or who died naturally, or touched a grave.

19On the third and seventh days the person who is ceremonially clean must sprinkle the water on those who are defiled. Then on the seventh day the people being cleansed must wash their clothes and bathe themselves, and that evening they will be cleansed of their defilement.