Exodus 19:11, 18, 20

and be ready by the third day, because on that day the LORD will come down on Mount Sinai in the sight of all the people.

Mount Sinai was covered with smoke, because the LORD descended on it in fire. The smoke billowed up from it like smoke from a furnace, and the whole mountain trembled violently.

The LORD descended to the top of Mount Sinai and called Moses to the top of the mountain. So Moses went up