大般涅槃經義記 6.371

6.371

不綺語中，佛語稱法無有綺異名「第一諦」，以言稱法「故無無義」明其語淨。

Regarding the absence of frivolous talk, the Buddha's speech matches reality and has no frivolous deviation, which is called "the ultimate truth"; because his words match reality, "therefore they are not without meaning," explaining the purity of his speech.