俱舍論記 22.43

22.43

「若諸樂受至壞時苦」者，此下答。明諸有漏行各由一苦，故成苦性。此顯三苦體性。若諸樂受，由壞滅位成苦性故。《正理》五十七釋經云「樂受生時住時樂者，由彼樂受性是樂故。壞時苦者，謂諸有情未離染時心恒求樂，於樂壞位起憂愁等，故說樂受為壞苦性。樂受壞時設無苦受，似苦顯現，亦名為苦（已上論文）。」

Regarding "If pleasant feelings... are suffering when undergoing destruction": below this is the answer. It clarifies that conditioned sāsrava phenomena, each by virtue of one [type of] suffering, become suffering by nature. This reveals the intrinsic nature of the three sufferings. If they are pleasant feelings, it is because they become suffering by nature at the time of their destruction. The Nyāyānusāra, fascicle fifty-seven, explains the sūtra: "'Pleasant feelings are pleasure when arising and when abiding' because that pleasant feeling is by nature pleasurable. 'They are suffering when undergoing destruction' means that when sentient beings have not yet separated from desire, their minds constantly seek pleasure; at the stage where pleasure is destroyed, grief and sorrow arise. Therefore, pleasant feelings are said to be of the nature of the suffering of change. When pleasant feeling is destroyed, even if there is no painful feeling, its manifesting as a semblance of suffering is also called suffering." (The above is the text of the treatise).