TAITTIRĪYA UPANISHAD · 3.5

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

vijñānaṃ brahmeti vyajānāt । vijñānāddhyeva khalvimāni
bhūtāni jāyante । vijñānena jātāni jīvanti ।
vijñānaṃ prayantyabhisaṃviśantīti । tadvijñāya ।
punareva varuṇaṃ pitaramupasasāra ।
adhīhi bhagavo brahmeti । taṃhovāca ।
tapasā brahma vijijñāsasva । tapo brahmeti ।
sa tapo’tapyata । sa tapastaptvā ।

He knew Knowledge for the Eternal. For from Knowledge alone, it appeareth, are these creatures born and being born they live by Knowledge and to Knowledge they go hence and return. And when he had known this, he came again to Varouna his father and said “Lord, teach me the Eternal.” But his father said to him “By askesis do thou seek to know the Eternal, for concentration of force is the Eternal.” He concentrated himself in thought and by the energy of his brooding

Sri Aurobindo · CWSA 18, p. 227