Deuteronomy 4:10-12

10Remember the day you stood before the Lord your God at Horeb, when the Lord said to me, ‘Assemble the people to Me, that I may let them hear My words 1so they may learn to 2fear Me all the days they live on the earth, and that they may 3teach their children.’

11You came near and stood at the foot of the mountain, 4and the mountain burned with fire to the very heart of the heavens: darkness, cloud and thick gloom.

12Then the Lord spoke to you from the midst of the fire; you heard the sound of words, but you saw no form--only a voice.