俱舍論疏 20.69

20.69

論「若爾何緣至而猶是有」，有部引經難也。若謂去、來全無體者，何故世尊說業過去而猶是有。故知去、來非無。

The Śāstra says: "If so, on what grounds... is nevertheless existing?": the Sarvāstivādins cite a sūtra to raise an objection. If you claim that the past and future have no substance at all, why did the World-Honoured One say that karma has passed away and yet still exists? Hence we know that the past and future are not non-existent.