Here is a good one from MN 59:
‘The ascetic Gotama spoke of the cessation of perception and feeling, and he includes it in happiness. What’s up with that?’
When wanderers who follow other paths say this, you should say to them, ‘Reverends, when the Buddha describes what’s included in happiness, he’s not just referring to pleasant feeling. The Realized One describes pleasure as included in happiness wherever it’s found, and in whatever context.’”
‘saññāvedayitanirodhaṁ samaṇo gotamo āha; tañca sukhasmiṁ paññapeti.
Tayidaṁ kiṁsu, tayidaṁ kathaṁsū’ti?Evaṁvādino, ānanda, aññatitthiyā paribbājakā evamassu vacanīyā: ‘na kho, āvuso, bhagavā sukhaṁyeva vedanaṁ sandhāya sukhasmiṁ paññapeti; api ca, āvuso, yattha yattha sukhaṁ upalabbhati yahiṁ yahiṁ taṁ taṁ tathāgato sukhasmiṁ paññapetī’”ti.
And here is AN 9.34 again:
“Extinguishment is bliss!”
When he said this, Venerable Udāyī said to him,
“But Reverend Sāriputta, what’s blissful about it, since nothing is felt?”“The fact that nothing is felt is precisely what’s blissful about it.”
“Sukhamidaṁ, āvuso, nibbānan”ti.
Evaṁ vutte, āyasmā udāyī āyasmantaṁ sāriputtaṁ etadavoca:
“kiṁ panettha, āvuso sāriputta, sukhaṁ yadettha natthi vedayitan”ti?“Etadeva khvettha, āvuso, sukhaṁ yadettha natthi vedayitaṁ.”
I suppose you could summarize these as the absence of suffering being happiness, which in this case means that the absence of feeling is preferable to feeling of any kind. This explains why the end rebirth is considered as happiness.