俱舍論記 22.79

22.79

「如有頌言至故說受皆苦」者，說一切有部答。頌中但依非常行苦、變壞壞苦說受皆苦，不依苦苦言受皆苦，明知別有樂受自性。若樂性苦，何不亦以苦苦觀耶？又解：無常、變壞俱是行苦。

As for "As a verse says... therefore it is said that feelings are all suffering": the Sarvāstivāda replies. In the verse, it only relies on the suffering of conditioned existence, which is non-eternity, and the suffering of deterioration, which is decay, to say that feelings are all suffering, and does not say that feelings are all suffering relying on the suffering of suffering; hence it is known that there is separately an intrinsic nature of pleasant feeling. If the nature of pleasure were suffering, why would one not also view it through the suffering of suffering? Another interpretation: Impermanence and deterioration are both the suffering of conditioned existence.