Exodus 19:11, 18, 20

and let them be ready for the third day, for on the third day the LORD will come down on Mount Sinai in the sight of all the people.

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 whole mountain quaked violently.

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.