Numbers 19:17-18

17For the purification of the unclean person, they are to take some of the ashes of the burnt sin offering, put them in a jar, and add fresh water to them.

18A person who is clean is to take hyssop, dip it in the water, and sprinkle the tent, all the furnishings, and the people who were there. He is also to sprinkle the one who touched a bone, a grave, a corpse, or a person who had been killed.