מדרש על עמוס 8:10

...The Rabbis say: God finds it hard to decree death upon the righteous. Whence this? For it is said, "Grievous in the sight of the Lord is the death of His saints (Psalms 116:15). And this is the proof. God should have spoken to Moses thus: "Behold you are about to die." God, however, did not speak in this way, but spared him and attached death to the days. Whence this? From what we read about the matter, "Behold, your days approach, to die."