俱舍論記 20.41

20.41

「何為不成至名過去」者，說一切有部救。何為不成？以有為法未已生名未來，若已生未已滅名現在，若已滅名過去。

Regarding "Why is it not established [...] called past": This is the Sarvāstivādin defense. Why is it not established? Because conditioned dharmas that have not yet been produced are called future; those that have been produced and have not yet ceased are called present; those that have already ceased are called past.