Leviticus 16:1-2

AFTER THE death of Aaron's two sons, when they drew near before the Lord [offered false fire] and died, [Lev. 10:1, 2.] The Lord said to Moses, Tell Aaron your brother he must not come at all times into the Holy of Holies within the veil before the mercy seat upon the ark, lest he die; for I will appear in the cloud on the mercy seat. [Heb. 9:7-15, 25-28.]