Which sutra does it say that someone like Buddha would "rest in jhana" or "go often resting" - some combination of jhana (not sure which stage) and rest. i saw it recently but I can't find it. I don't recall if the translation was from suttacentral.net or dhammatalk.org...
And what is the development of concentration that, when developed & pursued, leads to a pleasant abiding in the here & now? There is the case where a monk—quite withdrawn from sensuality, withdrawn from unskillful qualities—enters & remains in the first jhana: rapture & pleasure born from withdrawal, accompanied by directed thought & evaluation. With the stilling of directed thoughts & evaluations, he enters & remains in the second jhana: rapture & pleasure born of composure, unification of awareness free from directed thought & evaluation—internal assurance. With the fading of rapture, he remains equanimous, mindful, & alert, and senses pleasure with the body. He enters & remains in the third jhana, of which the Noble Ones declare, ‘Equanimous & mindful, he has a pleasant abiding.’ With the abandoning of pleasure & pain—as with the earlier disappearance of elation & distress—he enters & remains in the fourth jhana: purity of equanimity & mindfulness, neither pleasure nor pain. This is the development of concentration that, when developed & pursued, leads to a pleasant abiding in the here & now.
It may be, Cunda, that some monk, detached from sense-objects, detached from unsalutary ideas, enters into the first absorption that is born of detachment, accompanied by thought-conception and discursive thinking, and filled with rapture and joy, and he then might think: 'I am abiding in effacement.' But in the Noble One's discipline it is not these [attainments] that are called 'effacement'; in the Noble One's discipline they are called 'abidings in ease here and now.'
...It may be that after the stilling of thought conception and discursive thinking, he gains the inner tranquillity and harmony of the second absorption... in the Noble One's discipline they are called 'abidings in ease here and now.'
...Happily lives he who dwells in equanimity and is mindful!' — that third absorption he wins... in the Noble One's discipline they are called 'abidings in ease here and now.'
...he enters upon and abides in the fourth absorption...
...enters upon and abides in the sphere of infinite space...
...enters and abides in the sphere of infinite consciousness...
... enters and abides in the sphere of nothingness...
... enters and abides in the sphere of neither-perception-nor-non-perception; and he then might think: 'I am abiding in effacement.' But in the Noble One's discipline it is not these [attainments] that are called 'effacement'; in the Noble one's discipline they are called 'peaceful abidings'.
DN 16 (Ven. Sujato's translation):
I’m now old, elderly and senior. I’m advanced in years and have reached the final stage of life. I’m currently eighty years old. Just as a decrepit old cart keeps going by relying on straps,in the same way, the Realized One’s body keeps going as if it were relying on straps. Sometimes the Realized One, not focusing on any signs, and with the cessation of certain feelings, enters and remains in the signless immersion of the heart. Only then does the Realized One’s body become more comfortable.
The suttas say little about this meditation state. Its defining characteristic is that consciousness does not “follow after signs” (nimittānusāri viññāṇaṁ, eg. AN 6.13:5.3). This is explained in MN 138:10.2 as not being distracted or affected by the features of sense impressions. The mental unification (ekattaṁ) based on this practice is listed after the form (and formless) jhānas, so it is very advanced. It is nonetheless a conditioned state (MN 121:11.4), so it is possible that a mendicant might fall from it and disrobe (AN 6.60:8.10). However it may also be used to describe the meditation of an arahant (SN 41.7:6.12). It seems that the Buddha relied on his mastery of this practice to focus attention away from the pain in his body.
If one needs the word "rest" in the answer, note that there are many references to "restless" throughout the suttas, in the absence of which one would presumably be well rested. Restlessness and Jhana are incompatible.
MN43:20.3: When a mendicant has entered the first absorption, sensual desire, ill will, dullness and drowsiness, restlessness and remorse, and doubt are given up.