俱舍論疏 6.171

6.171

論「有一念業至如上應知」，明小三世，據滿說也。此中所以，如上應知。問：若爾，菩薩百劫修其相報業因，何唯一生受耶？答：修多加行助一業故，然正感者果多於因。

On the Śāstra's: "Karma of a single moment [...] should be understood as above": this clarifies the minor three time periods, stated in terms of fulfilling [karma]. The reason here should be understood as above. Question: If so, when a bodhisattva cultivates the causal karma for the marks and signs for a hundred kalpas, why is it experienced in only a single life? Answer: Because one cultivates many preparatory practices to assist a single karma; nevertheless, what is directly produced as result is greater than the cause.