From AN 9.34:
Ven: Sariputta: “Reverends, extinguishment (Nibbana) is bliss!
Ven. Udayi: “But Reverend Sāriputta, what’s blissful about it, since
nothing is felt?”
Ven. Sariputta: “The fact that nothing is felt is precisely what’s
blissful about it.
Sukha or happiness for an unenlightened person is experienced when encountering pleasant feelings (from the ...
Well it is most certainly based on these passages;
Take another mendicant who says: ‘I’ve developed the heart’s release
by compassion. I’ve cultivated it, made it my vehicle and my basis,
kept it up, consolidated it, and properly implemented it. Yet somehow
the thought of harming still occupies my mind.’ They should be told,
‘Not so, venerable! … For it is ...