俱舍論頌疏論本 15.59

15.59

釋曰：初一頌正明三受，次一頌引證，後一頌明順受。順樂苦非二者，標也。一順樂受業、二順苦受業、三順不苦不樂受業等，即非二也。

The commentary explains: The first stanza properly explains the three feelings, the second stanza cites proof, and the third stanza explains 'conducive to feeling'. "Conducive to pleasant, painful, and neither" is the heading. First, karma conducive to pleasant feeling; second, karma conducive to painful feeling; third, karma conducive to neither-painful-nor-pleasant feeling, which is 'neither'.