Numbers 19:17-19

Then for the unclean person they shall take some of the ashes of the burnt purification from sin and flowing water shall be added to them in a vessel. A 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 persons who were there, and on the one who touched the bone or the one slain or the one dying naturally or the grave. Then the clean person shall sprinkle on the unclean on the third day and on the seventh day; and on the seventh day he shall purify him from uncleanness, and he shall wash his clothes and bathe himself in water and shall be clean by evening.