Leviticus 16:1-3

Darby Translation

16 And Jehovah spoke to Moses after the death of the two sons of Aaron, when they came near before Jehovah and died;

² and Jehovah said to Moses, Speak unto Aaron thy brother, that he come not at all times into the sanctuary inside the veil before the mercy-seat which is upon the ark, that he die not; for I will appear in the cloud upon the mercy-seat.

³ In this manner shall Aaron come into the sanctuary: with a young bullock for a sin-offering, and a ram for a burnt-offering.