Numbers 19:19-20

19“The one who is clean is to sprinkle the unclean person on the third day and the seventh day. After he purifies the unclean person on the seventh day, the one being purified must wash his clothes and bathe in water, and he will be clean by evening.

20But a person who is unclean and does not purify himself, that person will be cut off from the assembly because he has defiled the sanctuary of the Lord. The water for impurity has not been sprinkled on him; he is unclean.