大般涅槃經義記 7.80

7.80

第三難中，初先汎明一切有法悉皆無常。「若涅槃」下約之顯法，「如佛昔」下引佛昔言明涅槃有。「以是義」下結成無常。

Regarding the third objection, first he generally clarifies that all existent dharmas are without exception impermanent. From "if nirvāṇa" downward applies it to reveal the dharma; from "as the Buddha formerly [said]" downward cites the Buddha's past words to show that nirvāṇa exists. From "by this meaning" downward concludes that it is impermanent.