俱舍論疏 6.286

6.286

論「共業生故」，答也。雖同業生，即有共業、不共業異。增上是共業故，所以共受；異熟非共業，不可共受。

The Śāstra states: "Because it is born from collective karma." This is the reply. Although all are produced from karma, there is the difference between collective karma and non-collective karma. Predominant [fruition] is due to collective karma, and is therefore collectively experienced; ripening is not collective karma, so it cannot be collectively experienced.