Exodus 19:14-19

14After Moses had gone down the mountain to the people, he consecrated them, and they washed their clothes.

15Then he said to the people, “Prepare yourselves for the third day. Abstain from sexual relations.” 16On the morning of the third day there was thunder and lightning, with a thick cloud over the mountain, and a very loud trumpet blast. Everyone in the camp trembled. 17Then Moses led the people out of the camp to meet with God, and they stood at the foot of the mountain. 18Mount Sinai was covered with smoke, because the LORD descended on it in fire. The smoke billowed up from it like smoke from a furnace, and the whole mountain Most Hebrew manuscripts; a few Hebrew manuscripts and Septuagint and all the people trembled violently.

19As the sound of the trumpet grew louder and louder, Moses spoke and the voice of God answered him. Or and God answered him with thunder