Śatapatha Brāhmaṇa ("of a hundred paths") 4.2.2.11

4.2.2.11

atha daśāpavitramupagṛhya hiṅkaroti | sā haiṣā vāganudyamānā tatāma tasyāṃ devā vāci tāntāyāṃ hiṅkāreṇaiva prāṇamadadhuḥ prāṇo vai hiṅkāraḥ prāṇo hi vai hiṅkārastasmādapigṛhya nāsike na hiṅkartuṃ śaknoti saitena prāṇena samajihīta yadā vai tāntaḥ prāṇaṃ labhate 'tha sa saṃjihīte tatho evaiṣa etadvāci tāntāyāṃ hiṅkāreṇaiva prāṇaṃ dadhāti saitena prāṇena saṃjihīte triṣkṛtvo hiṅkaroti trivṛddhi yajñaḥ

Having then wrapped up (the bowl in) a fringed filtering-cloth, he utters 'Hiṅ!' Now that same speech (Vâk, fem.), being unsupported, lay exhausted. By means of the 'Hiṅ' the gods infused breath into that exhausted speech, for the 'Hiṅ' is breath, the 'Hiṅ' is indeed breath: hence one cannot utter the sound 'hiṅ' after closing his nostrils. By means of that breath she rose again, for when one who is exhausted takes breath, he rises again. And in like manner does he now infuse breath into the exhausted speech by means of the 'Hiṅ,' and through. that breath she rises again. Thrice he utters the 'Hiṅ,' for threefold is the sacrifice.