俱舍論疏 5.156

5.156

論「若法令行至有為相中」，釋經不說住相所以。於中有二：一為住相不令有情怖故不說、二以住相濫無為故不說。此即初也，如文可知。

On the passage in the śāstra from “If a phenomenon causes formations…” to “…among the characteristics of the conditioned”: This explains the reason why the sūtra does not speak of the characteristic of duration. Therein are two points: first, it is not mentioned so that the characteristic of duration does not cause sentient beings to feel fear; second, it is not mentioned because the characteristic of duration might be confused with the unconditioned. This is the first, as is clear from the text.