大般涅槃經集解 39.112

39.112

案僧亮曰：偏難於空，明無相可得也。寶亮曰：涅槃是眾德上總名也。此三德唯一體，若是可得應是無常。何故？常法無得，有故非常也。

Sengliang says: This objects specifically regarding emptiness, clarifying that there are no marks to be attained. Baoliang says: Nirvāṇa is the general name for the myriad virtues. These three virtues are of a single essence; if they could be attained, they should be impermanent. Why? A permanent dharma is without attainment; existing [through attainment], it would not be permanent.