大般涅槃經集解 10.53

10.53

案僧亮曰：心馳萬境，故非定；寂然不動，故非不定也。僧宗曰：能大能小，故非定也；其體常湛，故非不定也。

Sengliang comments: The mind gallops across the myriad realms, hence it is not fixed; tranquil and unmoving, it is not unfixed. Sengzong says: Able to be great and able to be small, it is not fixed; its essence is ever clear and calm, hence it is not unfixed.