Gregory the Great — as excerpted in the Catena Aurea on Matthew 20:1-16

“(ubi sup.) And because the attainment of this kingdom is of the goodness of His will, it is added, Is it not lawful for me to do what I will with mine own? For it is a foolish complaint of man to murmur against the goodness of God. For complaint is not when a man gives not what he is not bound to give, but if he gives not what he is bound to give; whence it is added, Is thine eye evil because I am good?”