Exodus 19:17-19

17Moses led them out from the camp to meet with God, and they stood at the foot of the mountain.

18All 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.

19As the blast of the ram’s horn grew louder and louder, Moses spoke, and God thundered his reply.