Exodus 19:18-22

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

When the sound of the trumpet grew louder and louder, Moses spoke, and God answered him with thunder.

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

Then the Lord spoke to Moses: “Go down, warn the people, so that they do not break through to the Lord to stare, and many of them perish.

Also have the priests who approach the Lord consecrate themselves, or else the Lord will break out against them.”