Genesis 42:15

By the life of Pharaoh As sure as Pharaoh lives, or as I value the life of Pharaoh. A solemn protestation, as Judah, who heard it, and must have understood its meaning, explains it to his father, Genesis 43:3; The man did solemnly protest unto us. It seems, however, to have been the form of an oath in use among the Egyptians, as afterward the Romans used to swear by the name and life of their emperors. And it is no wonder that Joseph was carried by the stream of the general practice of the court, especially as the law of God concerning the appropriation of oaths unto God, that men are to swear only by his name, or are only to appeal to him for the truth of what they affirm, was not yet delivered.