成唯識論演祕 6.467

6.467

解云：業招生已雖有種子，後更不能招異熟果，其延壽法聖生淨居，皆資受果未盡之業。業若受果已盡之者，設得勝緣終不更能受於果也，故名有盡。若名言種為一業引生一期果，後逢緣引復能生果故名無盡，非無生果一期功能名無盡也。

The explanation says: After karma brings about a birth, although its bīja exists, it cannot again bring about a fruit of vipāka; the method of extending life and the noble ones' birth in the Śuddhāvāsa both nourish karma whose experience of fruit is not yet exhausted. If karma has already exhausted its experience of fruit, even if it encounters superior conditions, it can never again experience fruit; hence it is called exhaustible. If conventional bījas are projected by a karma to produce the fruit of a single lifespan, when they later encounter projecting conditions, they can again generate fruit; hence they are called inexhaustible. It is not that lacking the function of generating the fruit of a single lifespan is called inexhaustible.