俱舍論疏 22.185

22.185

論「隨在何世至通緣三世」，明緣世也。勝解作意唯於現境假想緣故，不緣過、未，如五識等唯緣現境。若過去緣過去，若現在緣現在，若未來生法緣未來，若不生法緣三世也。

The treatise says, "According with whichever time period it exists in... it universally focuses on the three time periods," which explains the time periods focused upon. Because mental application of resolve focuses only imaginatively on present objects, it does not focus on the past or future, just as the five consciousnesses focus only on present objects. If past, it focuses on the past; if present, it focuses on the present; if a future dharma destined to arise, it focuses on the future; if a dharma not destined to arise, it focuses on the three time periods.