成唯識論演祕 5.107

5.107

此釋伏難。「伏難」意云：有等流樂何名純苦？故今答云：望無異熟得純苦名。

This resolves a latent objection. The latent objection means: If there is flow-congruent (niṣyanda) pleasure, how can it be called pure suffering? Therefore it answers now: In view of the absence of pleasant karmic retribution (vipāka), it receives the name 'pure suffering.'