Exodus 19:16-19

16On the third day, when morning came, there was thunder and lightning. A thick cloud was upon the mountain, and a very loud blast of the ram’s horn went out, so that all the people in the camp trembled. 17Then Moses brought the people out of the camp to meet with God, and they stood at the foot of the mountain.

18Mount Sinai was completely enveloped in smoke, because the LORD had descended on it in fire. And the smoke rose like the smoke of a furnace, and the whole mountain quaked violently. 19And as the sound of the ram’s horn grew louder and louder, Moses spoke and God answered him in the thunder.