Leviticus 16:2
New International Version (NIV1984)
2 The Lord said to Moses: “Tell your brother Aaron not to come whenever he chooses into the Most Holy Place behind the curtain in front of the atonement cover on the ark, or else he will die, because I appear in the cloud over the atonement cover.
From BibleGateway.com: http://www.biblegateway.com/passage/?search=Leviticus 16:2&version=NIV1984
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