Deuteronomy 4:11-15

And ye came near and stood under the mountain; and the mountain burned with fire unto the midst of heaven, with darkness, clouds, and thick darkness.

And the LORD spake unto you out of the midst of the fire: ye heard the voice of the words, but saw no similitude; only ye heard a voice.

And he declared unto you his covenant, which he commanded you to perform, even ten commandments; and he wrote them upon two tables of stone.

And the LORD commanded me at that time to teach you statutes and judgments, that ye might do them in the land whither ye go over to possess it.

Take ye therefore good heed unto yourselves; for ye saw no manner of similitude on the day that the LORD spake unto you in Horeb out of the midst of the fire: