俱舍論疏 20.81

20.81

論「謂曾有當有至當有亦爾」，經部釋難也。若謂過、未同現有者，何故追憶彼時但憶曾有之相。逆觀亦爾。

The Śāstra says: "Namely, having once existed, or being bound to exist... bound to exist is also like this": the Sautrāntikas explain the objection. If you claim that the past and future exist in the same way as the present, why is it that when recollecting that time, one only recollects the aspect of 'having once existed'? Looking forward [to the future] is also like this.