Taittirīyopaniṣat 03.03

स तपोऽतप्यत। स तपस्तप्त्वा। प्राणो ब्रह्मेति व्यजानात्। प्राणाद्ध्येव खल्विमानि भूतानि जायन्ते। प्राणेन जातानि जीवन्ति। प्राणं प्रयन्त्यभिसंविशन्तीति। तद्विज्ञाय। पुनरेव वरुणं पितरमुपससार। अधीहि भगवो ब्रह्मेति। तगं होवाच। तपसा ब्रह्म विजिज्ञासस्व। तपो ब्रह्मेति ॥३॥

sa tapo'tapyata। sa tapastaptvā। prāṇo brahmeti vyajānāt। prāṇāddhyeva khalvimāni bhūtāni jāyante। prāṇena jātāni jīvanti। prāṇaṃ prayantyabhisaṃviśantīti। tadvijñāya। punareva varuṇaṃ pitaramupasasāra। adhīhi bhagavo brahmeti। taṃ hovāca। tapasā brahma vijijñāsasva। tapo brahmeti ॥3॥

[स (sa) - he; तपः (tapaḥ) - austerity; अतप्यत (atapyata) - practiced; स (sa) - he; तपः (tapaḥ) - austerity; तप्त्वा (taptvā) - having performed; प्राणः (prāṇaḥ) - prāṇa; ब्रह्म (brahma) - Brahman; इति (iti) - thus; व्यजानात् (vyajānāt) - understood; प्राणात् (prāṇāt) - from prāṇa; हि (hi) - indeed; एव (eva) - only; खलु (khalu) - indeed; इमानि (imāni) - these; भूतानि (bhūtāni) - beings; जायन्ते (jāyante) - are born; प्राणेन (prāṇena) - by prāṇa; जातानि (jātāni) - born; जीवन्ति (jīvanti) - live; प्राणम् (prāṇam) - prāṇa; प्रयन्ति (prayanti) - depart; अभिसंविशन्ति (abhisaṃviśanti) - merge; इति (iti) - thus; तत् (tat) - that; विज्ञाय (vijñāya) - having known; पुनः (punaḥ) - again; एव (eva) - indeed; वरुणम् (varuṇam) - Varuṇa; पितरम् (pitaram) - father; उपससार (upasasāra) - approached; अधीहि (adhīhi) - teach; भगवः (bhagavaḥ) - O venerable one; ब्रह्म (brahma) - Brahman; इति (iti) - thus; तं (taṃ) - to him; होवाच (hovāca) - said; तपसा (tapasā) - by austerity; ब्रह्म (brahma) - Brahman; विजिज्ञासस्व (vijijñāsasva) - seek to know; तपः (tapaḥ) - austerity; ब्रह्म (brahma) - Brahman; इति (iti) - thus;]

He practiced austerity. Having performed austerity, he realized that "prāṇa is Brahman." Indeed, from prāṇa alone all these beings are born; by prāṇa, the born live; into prāṇa they depart and merge. Having understood this, he again approached his father Varuṇa and said, "O venerable one, teach me Brahman." To him, Varuṇa replied, "Seek to know Brahman through austerity; austerity is Brahman."