Exodus 19:20-22

And Jehovah came down upon mount Sinai, to the top of the mount: and Jehovah called Moses to the top of the mount; and Moses went up. And Jehovah said unto Moses, Go down, charge the people, lest they break through unto Jehovah to gaze, and many of them perish. And let the priests also, that come near to Jehovah, sanctify themselves, lest Jehovah break forth upon them.