Yitro: Chapter 18
"There were thunders and lightnings"

The rabbis offer various ideas about "voices." One of them says that it means two voices - water and wind - which became one; one of them says that it is one voice that never ceases; one of them says that it comes from three - wind, water and fire. The discussion moves to lightning and then to the "fiery law" that is the Torah. And we learn that the sound of the Shofar came forth to break the heavy dark cloud.