Numbers 19:16-18, 20-21

Whoever in the open field touches someone who was killed with a sword or who died naturally, or touches a human bone or a grave, shall be unclean seven days. For the unclean they shall take some ashes of the burnt sin offering, and fresh water shall be added in a vessel. Then 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 whoever touched the bone, or the slain or the dead or the grave.

“If the man who is unclean does not cleanse himself, that person shall be cut off from the midst of the assembly, since he has defiled the sanctuary of the LORD. Because the water for impurity has not been thrown on him, he is unclean. And it shall be a statute forever for them. The one who sprinkles the water for impurity shall wash his clothes, and the one who touches the water for impurity shall be unclean until evening.