Exodus 19:18-21

18And mount Sinai was altogether on a smoke, because Yhwh descended upon it in fire: and the smoke thereof ascended as the smoke of a furnace, and the whole mount quaked greatly.

19And when the voice of the trumpet sounded long, and waxed louder and louder, Moses spake, and God answered him by a voice.

20And Yhwh came down upon mount Sinai, on the top of the mount: And Yhwh called Moses up to the top of the mount; and Moses went up.

21And Yhwh said unto Moses, Go down, charge the people, lest they break through unto Yhwh to gaze, and many of them perish.1