Exodus 19:17-21

And Moses brought forth the people out of the camp to meet with God; and they stood at the nether part of the mount.

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

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

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

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