Shatapatha Brahmana 11.1.2.3

11.1.2.3

ayaṃ vai yajño yo'yam pavate so'yameka ivaiva pavate so'yam puruṣe'ntaḥ praviṣṭo daśadhāvihitaḥ sa evam kLptaiḥ prāṇairagneryoneradhijāyate saiṣā daśākṣarā virāṭ saiṣā sampatsa yajñaḥ

And, indeed, this sacrifice is the blowing (wind): he blows here, as it were, as a single one, but when he has entered into man, he is divided into ten parts;--with the vital airs thus distributed, it (the sacrifice) is born from out of its womb, the fire: this is that Virâg of ten syllables, this is that perfection, the sacrifice.