Sikkha Sutta (AN 3:90)
“There are these three trainings. Which three? The training in heightened virtue, the training in heightened mind, the training in heightened discernment.
“And what is the training in heightened virtue? There is the case where a monk is virtuous. He dwells restrained in accordance with the Pāṭimokkha, consummate in his behavior & sphere of activity. He trains himself, having undertaken the training rules, seeing danger in the slightest fault. This is called the training in heightened virtue.
“And what is the training in heightened mind? There is the case where a monk—quite secluded from sensuality, secluded from unskillful qualities—enters & remains in the first jhāna: rapture & pleasure born of seclusion, accompanied by directed thought & evaluation. With the stilling of directed thoughts & evaluations, he enters & remains in the second jhāna: rapture & pleasure born of concentration, 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 jhāna, 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 jhāna: purity of equanimity & mindfulness, neither pleasure nor pain. This is called the training in heightened mind.
“And what is the training in heightened discernment? There is the case where a monk discerns as it has come to be that ‘This is stress… This is the origination of stress… This is the cessation of stress… This is the path of practice leading to the cessation of stress.’ This is called the training in heightened discernment.
“These are the three trainings.”