Numbers 19:18-20

18Then a man who is ceremonially clean is to take some hyssop, dip it in the water and sprinkle the tent and all the furnishings and the people who were there. He must also sprinkle anyone who has touched a human bone or a grave or anyone who has been killed or anyone who has died a natural death. 19The man who is clean is to sprinkle those who are unclean on the third and seventh days, and on the seventh day he is to purify them. Those who are being cleansed must wash their clothes and bathe with water, and that evening they will be clean. 20But if those who are unclean do not purify themselves, they must be cut off from the community, because they have defiled the sanctuary of the Lord. The water of cleansing has not been sprinkled on them, and they are unclean.