from Anguttara IX,iv,3 <A.iv,414>:
"The venerable Saariputta said this: 'Nibbaana is happiness, Friends, Nibbaana is happiness!' - When this was said, the venerable Udaayi said to the venerable Saariputta: 'But what is happiness, Friend Saariputta, since herein there is nothing felt [n'atthi vedayitan'ti]?' - 'Just this is happiness, Friend, that herein there is nothing felt,' [answered Venerable Saariputta]."
สัพเพ สัตตา สุขีตา โหนตุ
the mountain may be heavy in and of itself, but if you're not trying to carry it it's not heavy to you- Ajaan Suwat