Exodus 19:9

19:9 The Lord said to Moses, “I am going to come to you in a dense cloud, so that the people may hear when I speak with you and so that they will always believe in you.” And Moses told the words of the people to the Lord.

Exodus 19:19

19:19 When the sound of the horn grew louder and louder, Moses was speaking and God was answering him with a voice.