Numbers 19:17-18

And for the unclean, they are to take the dust of the burning of the sin-offering, and put flowing water on it in a vessel: And a clean person is to take hyssop and put it in the water, shaking it over the tent, and all the vessels, and the people who were there, and over him by whom the bone, or the body of one who has been put to death with the sword, or the body of one who has come to his end by a natural death, or the resting-place was touched.