Exodus 19:17-20

Then Moses led the people out of the camp to meet God, and they stood at the foot of the mountain. 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. The sound from the trumpet became louder. Then Moses spoke, and the voice of God answered him. 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.