Leviticus 16:16-18

16Through this process, he will purify the Most Holy Place, and he will do the same for the entire Tabernacle, because of the defiling sin and rebellion of the Israelites.

17No one else is allowed inside the Tabernacle when Aaron enters it for the purification ceremony in the Most Holy Place. No one may enter until he comes out again after purifying himself, his family, and all the congregation of Israel, making them right with the Lord.

18“Then Aaron will come out to purify the altar that stands before the Lord. He will do this by taking some of the blood from the bull and the goat and putting it on each of the horns of the altar.