Exodus 19:18-21

18Mount Sinai was wrapped in smoke because the Lord descended upon it in fire; its smoke ascended like the smoke of a furnace, and the whole mountain quaked violently.

19And it happened, as the blast of the ram’s horn grew louder and louder, Moses spoke and God answered him with [a voice of] thunder.

20The Lord came down on Mount Sinai, to the top of the mountain; and the Lord called Moses to the top of the mountain, and he went up.

21Then the Lord spoke to Moses, “Go down, warn the people, so that they do not break through [the barriers around the mountain] to the Lord to see [Me], and many of them perish [as a result].