And the LORD said to Moses: “Tell your brother Aaron not to enter freely into the Most Holy Place behind the veil in front of the mercy seat on the ark, or else he will die, because I appear in the cloud above the mercy seat.
Jewish Publication Society of America Version (JPS1917) - Leviticus 16:2 >and the LORD said unto Moses: 'Speak unto Aaron thy brother, that he come not at all times into the holy place within the veil, before the ark-cover which is upon the ark; that he die not; for I appear in the cloud upon the ark-cover.