Exodus 19:18-20

And mount Sinai was altogether on a smoke, because the LORD descended upon it in fire: and the smoke thereof ascended as the smoke of a furnace, and the whole mount quaked greatly. And when the voice of the trumpet sounded long, and waxed louder and louder, Moses spake, and God answered him by a voice. And the LORD came down upon mount Sinai, on the top of the mount: and the LORD called Moses up to the top of the mount; and Moses went up.