大方廣佛華嚴經隨疏演義鈔 61.38

61.38

疏「若智論」下，敘異釋也。前解定生，定在二禪。今云定生，定在初禪。背於初禪有覺觀定，得二禪故。欲界無定為可背故，初名離生。

Regarding the commentary's "If according to the Mahāprajñāpāramitopadeśa" downward: this recounts a differing explanation. The previous interpretation of 'born of concentration' placed concentration in the second dhyāna. Now, stating 'born of concentration', concentration is located in the first dhyāna. Because one turns one's back on the first dhyāna's concentration with vitarka and vicāra and attains the second dhyāna. Since the desire realm has no concentration to turn one's back upon, the first is called 'born of separation'.