Exodus 19:16-18

¹⁶So it came about on the third day, when it was morning, that there were thunder and lightning flashes and a thick cloud over the mountain and a very loud trumpet sound, so that all the people who were in the camp trembled. ¹⁷And Moses brought the people out of the camp to meet God, and they stood at the foot of the mountain.

¹⁸Now 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 entire mountain quaked violently.