Numbers 19:16-18, 20-21

Also, anyone in the open field who touches one who has been killed with a sword or who has died [of natural causes], or a human bone or a grave, shall be unclean for seven days. Then 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. 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 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.

‘But the man who is unclean and does not purify himself, that person shall be cut off from among the assembly, because he has defiled the sanctuary of the LORD. The water for purification has not been sprinkled on him; he is unclean. So it shall be a perpetual statute to them. He who sprinkles the water for impurity [on another] shall wash his clothes, and he who touches the water for impurity shall be unclean until evening.