Numbers 19:16-20

Also, anyone who in the open field touches one who has been killed with a sword or one who has died naturally, or touches a human bone or a grave, will be unclean for seven days.

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

And a clean person shall take hyssop and dip it in the water, and sprinkle it on the tent, on all the furnishings, on the persons 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.

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, and he shall wash his clothes and bathe himself in water and will be clean by evening.

‘But the person who is unclean and does not purify himself, that person shall be cut off from the midst of the assembly, because he has defiled the sanctuary of the Lord; the water for impurity has not been sprinkled on him, so he is unclean.