俱舍論頌疏論本 13.72

13.72

釋曰：勝義善解脫者，涅槃名解脫，以涅槃中最極安隱，眾苦都寂，猶如無病，是善是常，故名為勝；有實體故，復名為義，故此涅槃名勝義善。

The explanation says: "In the ultimate sense, wholesome is liberation": nirvāṇa is called liberation, because in nirvāṇa there is the supreme tranquility and all sufferings are completely pacified, just like being free from illness; it is wholesome and it is permanent, hence it is called 'ultimate'. Because it has real substantial existence, it is further called 'truth/reality'. Therefore, this nirvāṇa is called wholesome in the ultimate sense.