Numbers 19:9, 18

Now a man who is clean shall gather up the ashes of the heifer and deposit them outside the camp in a clean place, and the congregation of the sons of Israel shall keep it as water to remove impurity; it is purification from sin.

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.