Saṃyukta Āgama, Volume One, Sutra 1

The World-Honored One told the bhikṣus: You should engage in contemplative practice (vipaśyanā-caryā) on the impermanence of the aggregate of form (rūpa). One who can contemplate the impermanence of the aggregate of form as it truly is is engaged in correct contemplative practice. If one can correctly contemplate the impermanence of the aggregate of form, one will give rise to a mind of disenchantment toward the aggregate of form; when a mind of disenchantment arises toward the aggregate of form, one will eliminate the fondness and craving for the aggregate of form. One whose fondness and craving for the aggregate of form has been completely eliminated is one whose mind has been liberated.

Next, in the same way, contemplate the impermanence of the aggregate of feeling (vedanā), the aggregate of perception (saṃjñā), the aggregate of formations (saṃskāra), and the aggregate of consciousness (vijñāna). One who can contemplate the impermanence of these four aggregates—feeling, perception, formations, and consciousness—as they truly is engaged in correct contemplative practice. One who engages in correct contemplative practice will give rise to a mind of disenchantment toward these four aggregates of feeling, perception, formations, and consciousness; one who has given rise to a mind of disenchantment can completely eliminate the fondness and craving for these four aggregates. One whose fondness and craving for these four aggregates has been completely eliminated is one whose mind has been liberated.

Thus, bhikṣus, for one whose mind has been liberated, if he wishes to personally certify his liberation and his ability to enter nirvāṇa without remainder (anupadhiśeṣa-nirvāṇa), he can certify it himself, without needing others to certify it for him. He will certify it, saying: My birth-and-death through countless kalpas of saṃsāra has come to an end with this life; there will be no more birth and death. My pure brahma conduct has already been established; my mind has attained purity, and I no longer have desires or thoughts of craving. In this life, the work of liberating myself from birth and death that I set out to do has been completed. I myself know that I will not receive a body of desire-realm existence, a body of form-realm existence, or a body of formless-realm existence in future lives; I will not be reborn again within the three realms, and when my life ends, I will enter nirvāṇa without remainder.

The World-Honored One further told the bhikṣus: You should contemplate the suffering, emptiness, and not-self nature of the five aggregates (pañcaskandha). One who contemplates in this way is engaged in correct contemplative practice. One who can engage in correct contemplative practice will give rise to a mind of disenchantment toward the five aggregates; one who has given rise to a mind of disenchantment toward the five aggregates will eliminate the fondness and craving for the five aggregates. One whose fondness and craving for the five aggregates has been completely eliminated, I say, is one whose mind has been liberated. For one whose mind has been liberated, if he wishes to certify his own liberation, he can certify it himself. He will certify it, saying: Birth for me has been exhausted, brahma conduct has been established, what was to be done has been done, and I know for myself that there will be no further existence. At that time, the bhikṣus, having heard what the Buddha said, were all exceedingly joyful and received it with faith and put it into practice!