大般涅槃經集解 46.126

46.126

案僧亮曰：答第三難也。寶亮曰：地下之水，人不知故，謂之為無。穿掘必見，豈謂始有？涅槃真體，修善了出，非生因所造，豈無常耶？

Sengliang notes: Answering the third objection. Baoliang says: Because people do not know of the underground water, they call it non-existent. When they dig, they will certainly see it; how could it be called newly existent? The true substance of nirvāṇa is revealed through practicing goodness; it is not produced by a generative cause—how could it be impermanent?