大般涅槃經集解 66.34

66.34

案僧亮曰：第四難也。四難之意，皆責佛說不定也。智秀曰：第三引佛所說常教，為防難也。佛性若常，是則定法；若不定者，不得言常也。

Sengliang states: "This is the fourth objection. The import of these four objections is entirely to censure the Buddha's teachings as being indefinite." Zhixiu states: "The third adduces the teaching of permanence spoken by the Buddha to guard against objections. If the buddhadhātu is permanent, it is a determinate entity; if it is not determinate, it cannot be called permanent."