Pranavopanishat p3

p3

vasodvarāṇāmindranagaraṃ tadasurāḥ paryavārayanta | te devā bhītā āsana | ka imānasurān haniṣyatīti | tamoṅkāraṃ brahmaṇaḥ putraṃ jyeṣṭhaṃ dadṛśuste tamabruvan | bhavatā mukhyenemānasurān jayemeti | sa hovāca kiṃ me pratīvāho bhaviṣyatīti | varaṃ vṛṇīṣveti | vṛṇa iti | sa varamavṛṇīta | "na māmanīrayitvā brāhmaṇā brahma vadeyuryadi vadeyurabrahma tatsyāt" iti | tatheti te devā devayajanasyottarārdhe'suraiḥ saṃyattā āsaṃstānoṅkāreṇāgnīdhīyādevā asurān parābhāvayanta | tadyatparābhāvayanta tasmādoṅkāraḥ pūrvamuccāryate | yo ha vā etamoṅkāraṃ na vedāvaśyaḥ syādityatha ya evaṃ veda brahmavaśaḥ syāditi tasmādoṅkāra ṛgbhavati yajuṣi yajuḥ sāmni sāma sūtre sūtraṃ brāhmaṇe brāhmaṇaṃ loke ślokaḥ praṇave praṇava iti brāhmaṇam ||

Indra's city, [the abode] of the Vasus, had doors; the Asuras besieged it. The gods were afraid: "Who will slay these Asuras?" They saw that syllable Om, the eldest son of Brahman. They said to him: "With you as our leader, let us conquer these Asuras." He said: "What will be my reward?" "Choose a boon!" "I choose." He chose a boon: "Let the brahmins not recite sacred lore without first uttering me; if they should recite, it would be non-Brahman [and unholy]." "So be it." Those gods joined in battle with the Asuras on the northern half of the place of sacrifice; by means of the syllable Om from the Agnīdhra hearth, the gods defeated the Asuras. Because they defeated them, therefore the syllable Om is uttered first. Whoever indeed does not know this syllable Om becomes subject [to others]; and whoever knows it thus becomes master of Brahman. Therefore, the syllable Om becomes a Ṛc in the Ṛgveda, a Yajus in the Yajurveda, a Sāman in the Sāmaveda, a Sūtra in the Sūtra, a Brāhmaṇa in the Brāhmaṇa, a Śloka in ordinary speech, and a Praṇava in the Praṇava. Thus says the Brāhmaṇa.