Leviticus 16:1-2

New Revised Standard Version, Anglicised Catholic Edition

The Day of Atonement

16 The Lord spoke to Moses after the death of the two sons of Aaron, when they drew near before the Lord and died. ² The Lord said to Moses:

Tell your brother Aaron not to come just at any time into the sanctuary inside the curtain before the mercy-seat^[a] that is upon the ark, or he will die; for I appear in the cloud upon the mercy-seat.^[b]