The Yom Kippur Service
"And God spoke to Moses after the death of Aaron's two sons, who brought an (unauthorized) offering before the Lord and died. And God said to Moses: Speak to your brother Aaron, and let him not enter the holy place that is beyond the partition concealing the ark at any time, so that he may not die, since I appear over the ark cover in a cloud."
"Only thusly shall Aaron enter into the holy place: with a young bullock for a sin offering, and a ram for a burnt offering. He shall put on the sanctified white linen tunic, and have linen pants on his flesh. He shall gird himself with a linen sash, and bind his head with a linen turban. These are sacred vestments; before putting them on, he must immerse himself. And he shall take from the congregation of the children of Israel two goats for a sin offering, and one ram for a burnt offering. And Aaron shall offer the bullock of the sin offering which is for himself, and he shall make atonement for himself and for his family... " (Leviticus 16)