Taittirīyopaniṣat 03.05

स तपोऽतप्यत। स तपस्तप्त्वा। विज्ञानं ब्रह्मेति व्यजानात्। विज्ञानाद्ध्येव खल्विमानि भूतानि जायन्ते। विज्ञानेन जातानि जीवन्ति। विज्ञानं प्रयन्त्यभिसंविशन्तीति। तद्विज्ञाय। पुनरेव वरुणं पितरमुपससार। अधीहि भगवो ब्रह्मेति। तगं होवाच। तपसा ब्रह्म विजिज्ञासस्व। तपो ब्रह्मेति ॥५॥

sa tapo'tapyata। sa tapastaptvā। vijñānaṃ brahmeti vyajānāt। vijñānāddhyeva khalvimāni bhūtāni jāyante। vijñānena jātāni jīvanti। vijñānaṃ prayantyabhisaṃviśantīti। tadvijñāya। punareva varuṇaṃ pitaramupasasāra। adhīhi bhagavo brahmeti। taṃ hovāca। tapasā brahma vijijñāsasva। tapo brahmeti ॥5॥

[स (sa) - he; तपः (tapaḥ) - austerity; अतप्यत (atapyata) - practiced; स (sa) - he; तपः (tapaḥ) - austerity; तप्त्वा (taptvā) - having practiced; विज्ञानम् (vijñānam) - knowledge; ब्रह्म (brahma) - Brahman; इति (iti) - thus; व्यजानात् (vyajānāt) - he understood; विज्ञानात् (vijñānāt) - from knowledge; हि (hi) - indeed; एव (eva) - only; खलु (khalu) - indeed; इमानि (imāni) - these; भूतानि (bhūtāni) - beings; जायन्ते (jāyante) - are born; विज्ञानेन (vijñānena) - by knowledge; जातानि (jātāni) - born; जीवन्ति (jīvanti) - live; विज्ञानम् (vijñānam) - knowledge; प्रयन्ति (prayanti) - proceed; 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; तम् (tam) - him; होवाच (hovāca) - he said; तपसा (tapasā) - by austerity; ब्रह्म (brahma) - Brahman; विजिज्ञासस्व (vijijñāsasva) - seek to know; तपः (tapaḥ) - austerity; ब्रह्म (brahma) - Brahman; इति (iti) - thus;]

He performed austerities. After practicing austerity, he realized that "knowledge is Brahman." Indeed, it is from knowledge alone that all these beings arise; by knowledge, having been born, they live; and into knowledge they finally merge. Having understood this, he again approached his father Varuṇa and requested, "O revered one, teach me about Brahman." Varuṇa replied, "Seek to know Brahman through austerity; austerity itself is Brahman."