Numbers 19:12, 19

He must purify himself with water on the third day and on the seventh day, and so will be clean. But if he does not purify himself on the third day and the seventh day, then he will not be clean.

And the clean person must sprinkle the unclean on the third day and on the seventh day; and on the seventh day he must purify him, and then he must wash his clothes, and bathe in water, and he will be clean in the evening.