Bilangan 19:19

19:19 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, ¹  and then he must wash his clothes, and bathe in water, and he will be clean in the evening.

Bilangan 31:19

Purification After Battle

31:19 “Any of you who has killed anyone or touched any of the dead, remain outside the camp for seven days; purify yourselves and your captives on the third day, and on the seventh day.

¹ tn The construction uses a simple Piel of חָטָא (khata’, “to purify”) with a pronominal suffix – “he shall purify him.” Some commentators take this to mean that after he sprinkles the unclean then he must purify himself. But that would not be the most natural way to read this form.