ציטירנדיקער פּירוש אויף איוב 15:5

ואלהי יצחק AND THE GOD OF ISAAC — Although we do not find in the Scriptures that God associates his Name with that of the righteous whilst they are yet alive by writing, “The God of so-and-so”, — because it is said (Job 15:15) “Behold He putteth no trust even in His holy ones” — here, however, He associated his Name with that of Isaac because his eyes had become dim and he was confined to the house, so that he might be regarded as dead and as though the evil inclination had already passed away from him and he was unlikely to sin any more (Midrash Tanchuma, Toldot 7).