Bṛhadāraṇyaka Upaniṣad ("Great Forest Teaching") 1.6.3

1.6.3

atha karmaṇāmātmetyetadeṣāmukthamato hi sarvāṇi karmāṇyuttiṣṭhantyetadeṣām̐ sāmaitaddhi sarvaiḥ karmabhiḥ samametadeṣāṃ brahmaitaddhi sarvāṇi karmāṇi bibharti tadetattrayam̐ sadekamayamātmātmo ekaḥ sannetattrayaṃ tadetadamṛtam̐ satyena cchannaṃ prāṇo vā amṛtaṃ nāmarūpe satyaṃ tābhyāmayaṃ prāṇaśchannaḥ

Next, of the works, that which is called Body is the Uktha (hymn), for from it all works arise. It is their Sâman (song), for it is the same as all works. It is their Brahman (prayer), for it supports all works.
That being a triad is one, viz. this Self; and the Self, being one, is that triad. This is the immortal, covered by the true. Verily breath is the immortal, name and form are the true, and by them the immortal is covered.

1.6.3.p1

iti prathamādhyāye ṣaṣṭhaṃ brāhmaṇam

1.6.3.p2

iti prathamo'dhyāyaḥ