大般涅槃經義記 5.121

5.121

自下第三就受明苦，苦受之中備具三苦，先舉、後列：於苦受中違緣逼惱名為「苦苦」，緣壞致惱名為「壞苦」，厭行生惱名曰「行苦」。又心性是苦，於理性苦上加前三苦通名苦苦；即彼心體無常壞滅名為壞苦；即此心體遷流名行，行流不安名為行苦。又復前後無常破壞同名壞苦，同體四相虛集名行，虛集之行體無自性，自性無安名為行苦。餘之二受各具二苦，所謂行、壞，與向後門三苦之中行壞苦同。問曰：何故就受明苦？為彰昔日所說三受皆是苦故，今說為苦。

From here down is the third [part], clarifying suffering in terms of feeling. The feeling of suffering fully possesses all three sufferings; he first introduces and then enumerates them: within the feeling of suffering, oppression and affliction by contrary conditions is called the "suffering of suffering"; affliction caused by the destruction of conditions is called the "suffering of change"; and affliction born from wearying of conditioned activity is called the "suffering of conditioning." Furthermore, the nature of the mind is suffering; adding the previous three sufferings onto this suffering of the rational nature is collectively called the suffering of suffering. The impermanent destruction of that very mental essence is called the suffering of change. This very mental essence moving and flowing is called conditioned activity (saṃskāra); the instability of its conditioned flow is called the suffering of conditioning. Furthermore, earlier and later impermanent destruction is collectively called the suffering of change; the empty assemblage of the four characteristics within the same essence is called conditioned activity; the essence of such empty, assembled conditioned activity lacks self-nature, and this lack of rest in its self-nature is called the suffering of conditioning. The other two feelings each possess two sufferings, namely conditioning and change, which are identical to the suffering of conditioning and the suffering of change among the three sufferings in the latter approach mentioned above. Question: Why is suffering clarified in terms of feeling? It is to reveal that the three feelings spoken of formerly are all suffering, so they are now spoken of as suffering.