Exodus 19:18-19
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18And mount Sinai, the whole of it, smoked, because Jehovah 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 waxed louder and louder, Moses spake, and God answered him by a voice.
Exodus 19:18-19 (ASV)