Numbers 19:18-19

18Then a person who is clean must take hyssop. He must put it into the water. Then he must use it to splash the water on the tent and on everything that is in it. He must also splash the water on all the people who have been there. And he must splash it on the person who touched the bone or the dead body or the grave.

19And the clean person must splash the water on the unclean person on the third day too. And he must do it on the seventh day. On the seventh day he will make the person clean again. Then the person who had not been clean must wash his clothes. And he must wash himself in water. In the evening, that person will become clean.