Numbers 19:18-19

18A person who is clean will take a sprig of hyssop, dip it in the water, and sprinkle the tent, all the furnishings, and all the people who were in the tent ⌞with the dead body⌟. He must also sprinkle any person who has touched a human bone or a grave and any person who has touched someone who has been killed or who has died naturally.

19A person who is clean will sprinkle these types of unclean people on the third day and the seventh day. On the seventh day the clean person will finish taking away their sins. Then they must wash their clothes and bodies, and in the evening they will be clean.