俱舍論疏 24.30

24.30

On the treatise passage, "As for the one who goes upstream... only then attains parinirvāṇa": This explains the one who goes upstream (ūrdhvasrotas). Herein there are two parts: first, a general explanation; second, a specific explanation. This text is the general explanation. "Goes upstream" means "proceeding upward." As for the former who attains parinirvāṇa upon rebirth, although they are reborn in an upper realm, they attain parinirvāṇa right in that place of rebirth and do not take further rebirth higher up; they lack the meaning of proceeding upward, which is why those who attain parinirvāṇa upon rebirth and so forth are not called "upstream." If, having been reborn in the form realm, one must successively take birth higher up, all such are called "upstream," because there is upward progression.