Exodus 19:16-20

So it came about on the third day, when it was morning, that there were thunder and lightning flashes and a thick cloud upon the mountain and a very loud trumpet sound, so that all the people who were in the camp trembled. And Moses brought the people out of the camp to meet God, and they stood at the foot of the mountain. ORD Now Mount Sinai was all in smoke because the LORD descended upon it in fire; and its smoke ascended like the smoke of a furnace, and the whole mountain quaked violently. When the sound of the trumpet grew louder and louder, Moses spoke and God answered him with thunder. The LORD came down on Mount Sinai, to the top of the mountain; and the LORD called Moses to the top of the mountain, and Moses went up.