Exodus 19:18-19
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18And mount Sinai was altogether on a smoke, because the LORD descended upon it in fire: and the smoke thereof ascended as the smoke of a furnace, and the whole mount quaked greatly. 19And when the voice of the trumpet sounded long, and waxed louder and louder, Moses spake, and God answered him by a voice.
Exodus 19:18-19 (KJV)