Numbers 19:19-20

And the clean person shall sprinkle it on the unclean on the third day and on the seventh day. Thus on the seventh day he shall cleanse him, and he shall wash his clothes and bathe himself in water, and at evening he shall be clean. “If the man who is unclean does not cleanse himself, that person shall be cut off from the midst of the assembly, since he has defiled the sanctuary of the LORD. Because the water for impurity has not been thrown on him, he is unclean.