Brihadaranyaka Upanishad 3.1.5

3.1.5

yājñavalkyeti hovāca yadidam̐ sarvaṃ pūrvapakṣāparapakṣābhyāmāptam̐ sarvaṃ pūrvapakṣāparapakṣābhyāmabhipannaṃ kena yajamānaḥ pūrvapakṣāparapakṣayorāptimatimucyata ityudgātrartvijā vāyunā prāṇena prāṇo vai yajñasyodgātā tadyo'yaṃ prāṇaḥ sa vāyuḥ sa udgātā sa muktiḥ sātimuktiḥ

‘Yâjnavalkya,’ said he, ‘since all this is overtaken by the bright and dark fortnights, and swayed by them, by what means does the sacrificer go beyond the bright and dark fortnights?’ ‘Through the vital force—through air, which is the (real) priest called Udgâtri.footnote{Who chants hymns from the Sâma-Veda.} The vital force of the sacrificer is the Udgâtri. This vital force is air, and it is the Udgâtri; this (air) is liberation; this (liberation) is emancipation.’