Targum zu Schemot 20:2

The first word, as it came forth from the mouth of the Holy One, whose Name be blessed, was like storms, and lightnings, and flames of fire, with a burning light on His right hand and on His left. It winged its way through the air of the heavens, and was made manifest unto the camp of Israel, and returned, and was engraven on the tables of the covenant that were given by the hand of Mosheh, and were turned in them from side to side: and then called He, and said: Sons of Israel My people, I am the Lord your God, who brought you out free from the land of Mizraim, from the house of the bondage of slaves.