Deuteronomy 4:12

4:12 Then the Lord spoke to you from the middle of the fire; you heard speech but you could not see anything – only a voice was heard. ¹ 

Deuteronomy 4:33

4:33 Have a people ever heard the voice of God speaking from the middle of fire, as you yourselves have, and lived to tell about it?

[4:12]  ¹ tn The words “was heard” are supplied in the translation to avoid the impression that the voice was seen.