Leviticus 16:15-17

15Aaron shall then slaughter the goat for the sin offering for the people and bring its blood behind the veil, and with its blood he must do as he did with the bull’s blood: He is to sprinkle it against the mercy seat and in front of it.

16So he shall make atonement for the Most Holy Place because of the impurities and rebellious acts of the Israelites in regard to all their sins. He is to do the same for the Tent of Meeting which abides among them in the midst of their impurities. 17No one may be in the Tent of Meeting from the time Aaron goes in to make atonement in the Most Holy Place until he leaves, after he has made atonement for himself, his household, and the whole assembly of Israel.