Exodus 19:16; Exodus 19:19; Exodus 20:18

16 So it came about on the third day, when it was morning, that there were thunder and lightning flashes and a thick cloud upon the mountain and a very loud trumpet sound, so that all the people who were in the camp trembled.

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

18 All the people perceived the thunder and the lightning flashes and the sound of the trumpet and the mountain smoking; and when the people saw it, they trembled and stood at a distance.