R. Yitzchak says: (A verse) is not necessary (to tell us that left-overs of the Pesach may not be burned on the festival). For if the burning of chametz, which is interdicted in being seen or being found, does not override the festival, how much more so should the burning of the left-overs of the Pesach not override the festival. What, then, is the intent of "until morning"? As stated above.