大般涅槃經義記 5.117

5.117

名義如是，體相云何？分別有四：一當相分別，如彼《成實．受相品》說損減身心名為苦受、增益身心名為樂受、非損非益名不苦不樂。

Such are the names and meanings; what are their essences and characteristics? There are four distinctions: First, distinguishing according to their intrinsic marks: as explained in the *Tattvasiddhi-śāstra*'s "Chapter on the Marks of Feeling", diminishing body and mind is called the feeling of suffering, benefiting body and mind is called the feeling of pleasure, and neither diminishing nor benefiting is called neither-suffering-nor-pleasure.