Numbers 19:4, 19

And Eleazar the priest shall take some of its blood with his finger, and sprinkle some of its blood toward the front of the tent of meeting seven times.

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.