Leviticus 16:1-2

1The Lord spoke to Moses after the two sons of Aaron died. The gift that they gave to the Lord was not holy. So they died.

2The Most Holy Place in the Tent of Meeting is behind the curtain. The Lord said to Moses, ‘Your brother Aaron cannot go behind the curtain at any time that he wants to. Tell him that. The Lord appears in a cloud over the lid of the Covenant Box. So Aaron will die if he does not obey the Lord.