Numbers 19:19-20

19Then the clean person shall sprinkle [the water for purification] on the unclean person on the third day and on the seventh day, and on the seventh day the unclean man shall purify himself, and wash his clothes and bathe himself in water, and shall be [ceremonially] clean at evening.

20‘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 for purification has not been sprinkled on him; he is unclean.