When Moses saw that neither the world nor mankind could aid him, he betook himself to the Angel of the Face, to whom he said, "Pray for me, that God may take pity upon me, and that I may not die." But the angel replied: "Why, Moses, dost thou exert thyself in vain? Standing behind the curtain that is drawn before the Lord, I heard that thy prayer in this instance is not to be answered." Moses now laid his hand upon his head and wept bitterly, saying, "To whom shall I now go, that he might implore God's mercy for me?"
Moses Begs the Angel of the Face to Save Him
Legends of the Jews 6:151