Numbers 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.

Numbers 31:23

31:23 everything that may stand the fire, you are to pass through the fire, ²  and it will be ceremonially clean, but it must still be purified with the water of purification. Anything that cannot withstand the fire you must pass through the water.

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.

² sn Purification by fire is unique to this event. Making these metallic objects “pass through the fire” was not only a way of purifying (burning off impurities), but it seems to be a dedicatory rite as well to the Lord and his people. The aspect of passing through the fire is one used by these pagans for child sacrifice.