俱舍論疏 15.20

15.20

論「言支定者至當持不犯」，釋支定也。謂若五戒、二百五十戒等，於中隨簡一戒，云不能持，即不戒發。

On the Śāstra's: "The statement 'the limitation of branches'... shall uphold without violating", this explains the limitation of branches. That is, if among the five precepts, the two hundred and fifty precepts, and so forth, one singles out any one precept and says one cannot uphold it, then the discipline does not arise.