Exodus 19:18-20

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. As the blast of the ram’s horn grew louder and louder, Moses spoke, and God thundered his reply. The LORD came down on the top of Mount Sinai and called Moses to the top of the mountain. So Moses climbed the mountain.