Exodus 19:18-21

18And mount Sinai was altogether in a smoke, because the LORD descended upon it in fire: and the smoke of it ascended as the smoke of a furnace, and the whole mount trembled greatly. 19And when the voice of the trumpet sounded long, and grew louder and louder, Moses spoke, and God answered him by a voice. 20And the LORD came down upon mount Sinai, on the top of the mount: and the LORD called Moses to the top of the mount; and Moses went up. 21And the LORD said to Moses, Go down, charge the people, lest they break through to the LORD to gaze, and many of them perish.1