Targum zu Schemot 4:20

And Mosheh took his wife and his sons, and made them ride on the ass, and returned to the land of Mizraim. And Mosheh took the rod which he had brought away from the chamber of his father-in-law; and it was from the sapphire Throne of glory, in weight forty sein; and upon it was engraven and set forth the Great and Glorious Name by which the signs should be wrought before the Lord by his hand.