Numbers 19:17-19

¹⁷And they shall take of the ashes of the burning and of the sin offering, and shall pour living waters upon them into a vessel.

¹⁸And a man that is clean shall dip hyssop in them, and shall sprinkle therewith all the tent, and all the furniture, and the men that are defiled with touching any such thing:

¹⁹And in this manner he that is clean shall purify the unclean on the third and on the seventh day. And being expiated the seventh day, he shall wash both himself and his garments, and be unclean until the evening.