Numbers 19:16-18, 20-21

Also, anyone who in the open field touches one who has been slain with a sword or who has died naturally, 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 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.

‘But the man who is unclean and does not purify himself from uncleanness, 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, he is unclean. So it shall be a perpetual statute for them. And he who sprinkles the water for impurity shall wash his clothes, and he who touches the water for impurity shall be unclean until evening.