Taittiriya Upanishad 3.1.1

3.1.1

āūṃ saha nāvavatu /
saha nau bhunaktu /
saha vīryaṃ karavāvahai /
tejasvi nāvadhītamastu mā vidviṣāvahai /
āūṃ śāntiḥ śāntiḥ śāntiḥ //
bhṛgurvai vāruṇiḥ /
varuṇaṃ pitaramupasasāra /
adhīhi bhagavo brahmeti /
tasmā etatprovāca /
annaṃ prāṇaṃ cakṣuḥ śrotraṃ mano vācamiti /
tam̐ hovāca /
yato vā imāni bhūtāni jāyante /
yena jātāni jīvanti /
yatprayanyabhisam̐viśanti /
tadvijijñāsasva /
tadbrahmeti /
sa tapo 'tapyata /
sa tapastaptvā // 1//
iti prathamo 'nuvākaḥ //

Bhṛgu, the well-known son of Varuṇa, approached his father Varuṇa with the (formal) request, "O, revered sir, teach me Brahman". To him he (Varuṇa) said this: "Food, vital force, eye, ear, mind, speech—(these are the aids to knowledge of Brahman)." To him he (Varuṇa) said: "Crave to know that from which all these beings take birth, that by which they live after being born, that towards which they move and into which they merge. That is Brahman." He practised concentration. He, having practised concentration,