Numbers 19:9, 18

And a man who is clean shall gather up the ashes of the heifer and deposit them outside the camp in a clean place. And they shall be kept for the water for impurity for the congregation of the people of Israel; it is a sin offering.

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.