Numbers 19:18-19

18A clean person shall take hyssop and dip it in the water and sprinkle it on the tent and on all the furnishings and on the people who were there, and on the one who touched the bone or the one who was killed or the one who died [naturally] or the grave.

19Then the clean person shall sprinkle [the water for purification] on the unclean person on the third day and on the seventh day, and on the seventh day the unclean man shall purify himself, and wash his clothes and bathe himself in water, and shall be [ceremonially] clean at evening.