Saṃyutta Nikāya 45
Connected Discourses on the Path
29. Feeling
At Savatthī. “Bhikkhus, there are these three feelings. What three? Pleasant feeling, painful feeling, neither-painful-nor-pleasant feeling. These are the three feelings.
“The Noble Eightfold Path, bhikkhus, is to be developed for the full understanding of these three feelings. What is the Noble Eightfold Path? It is: right view … right concentration. The Noble Eightfold Path is to be developed for the full understanding of these three feelings.”