俱舍論記 26.128

26.128

「先未曾得至俱決定故」者，答。先未曾得此種姓故，今時創得勢力未廣，故修同類不能傍修。又諸忍、智，對治決定、所緣決定，唯修同類不能傍修。如苦忍、苦智決定對治苦下煩惱，決定以苦諦為所緣境。如是乃至道忍、道智應知亦爾。故《婆沙》一百七云「復次以見道所緣定、對治定故，唯修同分。修道所緣不定、對治不定故，能修同分、不同分。」

On the passage beginning with "Because it was never previously acquired ... because both are determined": this is the answer. Because one has never previously acquired this lineage, and now that it is newly acquired its power is not yet extensive, it therefore cultivates its own kind and cannot cultivate collaterally. Furthermore, for all tolerances and cognitions, their antidotes are determined and their cognitive objects are determined; thus they cultivate only their own kind and cannot cultivate collaterally. For example, the tolerance of suffering and the cognition of suffering definitively counter the defilements under suffering, and definitively take the truth of suffering as their cognitive object. Up to the tolerance of the path and the cognition of the path, one should know that it is likewise. Therefore, the one hundred and seventh fascicle of the Mahāvibhāṣā states: "Furthermore, because the cognitive objects and antidotes of the path of seeing are determined, it cultivates solely its own class. Because the cognitive objects and antidotes of the path of cultivation are not determined, it is capable of cultivating both its own class and different classes."