Exodus 19:11, 18, 20

Be sure they are ready on the third day, for on that day the LORD will come down on Mount Sinai as all the people watch.

All of Mount Sinai was covered with smoke because the LORD had descended on it in the form of fire. The smoke billowed into the sky like smoke from a brick kiln, and the whole mountain shook violently.

The LORD came down on the top of Mount Sinai and called Moses to the top of the mountain. So Moses climbed the mountain.