Numbers 19:17-18

17Then for the unclean person they shall take some of the ashes of the heifer burnt for the purification from sin, and running water shall be added to them in a container.

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.