大般涅槃經義記 2.127

2.127

自下第三釋無變異。迦葉初先舉闇無影，欲令如來同之變異；下佛答之，明影常有，顯佛無變。於中先明如來恒有，無眼不具，先喻、後合。「如彼闇」下，明諸眾生不見時節，先喻、後合。「佛滅度後」合彼闇時，「說言無常」合不見影。

From here on, the third [part] explains non-alteration. Kāśyapa first adduces darkness lacking a shadow, wishing to make the Tathāgata assimilate to alteration; below, the Buddha replies to him, clarifying that the shadow always exists, revealing that the Buddha has no alteration. Within this, he first clarifies that the Tathāgata constantly exists, and there are none whose eyes are incomplete—first the analogy, and afterwards the application. From "Like that darkness..." onwards, he clarifies the times when sentient beings do not see—first the analogy, and afterwards the application. "After the Buddha has passed into extinction" applies to that time of darkness; "saying that he is impermanent" applies to not seeing the shadow.