MN 44 Cūḷa Vedalla Sutta: The Shorter Series of Questions and Answers
Bhikkhuni Dhammadina, an arahant, talks with her former husband Visakha, a non-returner.
“..pleasant feeling is pleasant when it persists and painful when it changes.
Painful feeling is painful when it persists and pleasant when it changes.
Neither-painful-nor-pleasant feeling is pleasant when there is knowledge of it and painful when there is no knowledge of it.”