Leviticus 16:2,3
And the LORD said to Moses, Speak to Aaron your brother, that he come not at all times into the holy place within the veil before the mercy seat, which is on the ark; that he die not: for I will appear in the cloud on the mercy seat.
Torrey's Topical Textbook—AKJV

Hebrews 9:7
But into the second went the high priest alone once every year, not without blood, which he offered for himself, and for the errors of the people:
Torrey's Topical Textbook—AKJV