Exodus 19:17-19

And Moses brought forth the people out of the camp to meet God; and they stood at the nether part of the mount. And mount Sinai, the whole of it, smoked, because Jehovah 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 waxed louder and louder, Moses spake, and God answered him by a voice.