俱舍論疏 22.75

22.75

論「以諸樂因至理亦應然」，答理也。以此樂因不定為理。既此樂因後生其苦，故知根本亦是苦因。初微不覺第一理也。

On the Śāstra's statement, "Because all causes of pleasure... reasoning should also be thus": They reply with the reasoning. They take these causes of pleasure being unfixed as the reasoning. Since this cause of pleasure later produces suffering, one therefore knows that fundamentally it is also a cause of suffering. That at first, being subtle, it is not perceived, is the first reasoning.