Leviticus 16:32-34

In future generations, the purification ceremony will be performed by the priest who has been anointed and ordained to serve as high priest in place of his ancestor Aaron. He will put on the holy linen garments and purify the Most Holy Place, the Tabernacle, the altar, the priests, and the entire congregation. This is a permanent law for you, to purify the people of Israel from their sins, making them right with the LORD once each year.” Moses followed all these instructions exactly as the LORD had commanded him.