[412] How does one train thus: 'Experiencing the mind (citta) (cittapaṭisaṃvedī), I shall breathe out'; how does one train thus: 'Experiencing the mind, I shall breathe in'?
What is that mind? By way of the long out-breath, the consciousness-mind (viññāṇacitta): that which is mind (citta), mentality (mano), mentation (mānasa), heart (hadaya), the lucid (paṇḍara), the mind base (manāyatana), the mind faculty (manindriya), consciousness (viññāṇa), the consciousness aggregate, and the corresponding mind-consciousness element (tajjā manoviññāṇadhātu); by way of the long in-breath … tranquilizing the mental formation (cittasaṅkhāra), by way of the out-breath, the consciousness-mind: that which is mind, mentality, mentation, heart, the lucid, the mind base, the mind faculty, consciousness, the consciousness aggregate, and the corresponding mind-consciousness element — this is the mind.
How is that mind known (paṭividita)? For one who knows the unification of mind and non-distraction by way of the long out-breath, mindfulness is established; by means of that mindfulness and that knowledge (ñāṇa) that mind is known. For one who knows the unification of mind and non-distraction by way of the long in-breath, mindfulness is established; by means of that mindfulness and that knowledge the mind is known. … For one realizing what is to be realized, that mind is known. Thus is that mind known. The consciousness-mind, by way of the breath experiencing the mind, [is what appears]: the establishment (upaṭṭhāna) is mindfulness; the contemplation is knowledge. The mind is the establishment, but it is not the mindfulness; mindfulness is both the establishment and the mindfulness. By means of that mindfulness and that knowledge one contemplates that mind. Therefore it is said: 'the development of the establishment of mindfulness (satipaṭṭhāna) as contemplation of the mind in the mind.'
'Contemplates': how does one contemplate that mind? … Thus does one contemplate that mind.
'Development' (bhāvanā): there are four kinds of development … development in the sense of repeated practice. The out-breaths and in-breaths of one experiencing the mind are purity of virtue (sīlavisuddhi) in the sense of restraint … For one who knows the unification of mind and non-distraction by way of the out-breaths and in-breaths of one experiencing the mind … knowing, one brings the faculties (indriya) together; therefore it is said: 'and one penetrates that whose meaning is calm (samattha).'
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.