Numbers 19:19-20

The clean person shall sprinkle the unclean on the third day and on the seventh day; and on the seventh day he shall purify himself, wash his clothes, and bathe in water; and at evening he shall be clean. ‘But the man who is unclean and does not purify himself, that person shall be cut off from among the assembly, because he has defiled the sanctuary of the LORD. The water of purification has not been sprinkled on him; he is unclean.