俱舍論記 28.47

28.47

「然契經中至非永出故」者，說一切有部通大眾等伏難。伏難意云：經中既言有不出有，明知無色有不能出色有。若能出者，應言有出有。為通此伏難，故釋斯經。然契經中說三有不能出三有者，為自地惑之所縛故，故言於自地有不能出故。但離八地非離有頂故，故言非遍出故。凡夫斷惑後還退故，故言非永出故。是故經言有不出有，不言無色有不能出色有。

Regarding 'However, in the sūtras... not being permanent emergence': the Sarvāstivāda resolves an implicit objection raised by the Mahāsāṃghika and others. The implicit objection means: 'Since the sūtras say that existence cannot emerge from existence, it is clear that formless existence cannot emerge from form existence. If it could emerge, one should say existence emerges from existence.' To resolve this implicit objection, the text explains this sūtra: however, when the sūtras say that the three existences cannot emerge from the three existences, it is because one is bound by the defilements of one's own stage; hence it says 'because one cannot emerge from existence of one's own stage.' It is only separation from eight stages, not separation from the peak of existence; hence it says 'because it is not an all-pervading emergence.' Because ordinary persons backslide after severing defilements, it says 'because it is not a permanent emergence.' Therefore the sūtra says 'existence does not emerge from existence'; it does not say that formless existence cannot emerge from form existence.