Exodus 19:11, 18, 20

and be ready by the day after tomorrow. On that day I, the LORD, will come down on Mount Sinai, and all the people will see me.

Mount Sinai was covered with smoke, because the LORD came down on it in fire. The smoke rose from the mountain like smoke from a furnace, and the whole mountain shook wildly.

When the LORD came down on top of Mount Sinai, he called Moses to come up to the top of the mountain, and Moses went up.