Numbers 19:6, 18

and the priest shall take cedar-wood, and hyssop, and scarlet, and cast it into the midst of the burning of the heifer.

and a clean person shall take hyssop, and dip it in the water, and sprinkle it upon the tent, and upon all the vessels, and upon the persons that were there, and upon him that touched the bone, or the slain, or the dead, or the grave