Rashi on Deuteronomy 31:29/רש"י על דברים ל״א:כ״ט

1אחרי מותי כי השחת תשחתון [FOR I KNOW THAT] AFTER MY DEATH YE WILL UTTERLY CORRUPT YOURSELVES — But, you see, as a matter of fact, that all the days of Joshua they did not corrupt themselves, for it states, (Judges 2:7) “And the people served the Lord all the days of Joshua”?! (How, then, could Moses say that they would corrupt themselves after his death, by which he evidently meant immediately after his death, cf. v. 16)? But we may derive from here that one’s pupil should be as dear to him as his own self: — it appeared to Moses that so long as Joshua would live it would be as though he himself would be living (he thus alluded by the words “after my death” to a period after Joshua’s death).