Leviticus 16:31-34

16:31 It is to be a Sabbath of complete rest for you, and you must humble yourselves. It is a perpetual statute.

16:32 “The priest who is anointed and ordained to act as high priest in place of his father is to make atonement. He is to put on the linen garments, the holy garments, 16:33 and he is to purify the Most Holy Place, he is to purify the Meeting Tent and the altar, and he is to make atonement for the priests and for all the people of the assembly. 16:34 This is to be a perpetual statute for you to make atonement for the Israelites for all their sins once a year.” So he did just as the Lord had commanded Moses.