俱舍論疏 6.170

6.170

論「有一世業至果減因故」，就大三世明也。如一世造業可三世受，無三世造業同一世受，據引說也。勿設劬勞，果少因故。

On the Śāstra's: "Karma of a single lifetime [...] because the result would be less than the cause": this is explained in terms of the major three time periods. Just as karma created in a single lifetime can be experienced across three lifetimes, there is no karma created in three lifetimes that is experienced in the same single lifetime, which is stated in terms of projecting [karma]. Lest one exert toil and the result be less than the cause.