Bṛhadāraṇyaka Upaniṣad ("Great Forest Teaching") 3.5.1

3.5.1

atha hainaṃ kaholaḥ kauṣītakeyaḥ papraccha yājñavalkyeti hovāca yadeva sākṣādaparokṣādbrahma ya ātmā sarvāntarastaṃ me vyācakṣvetyeṣa ta ātmā sarvāntaraḥ katamo yājñavalkya sarvāntaro yo'śayanāyāpipāse śokaṃ mohaṃ jarāṃ mṛtyumatyeti | etaṃ vai tamātmānaṃ viditvā brāhmaṇāḥ putraiṣaṇāyāśca vittaiṣaṇāyāścalokaiṣaṇāyāśca vyutthāyātha bhikṣācaryaṃ caranti yā hyeva putraiṣaṇā sā vittaiṣaṇāyā vittaiṣaṇā sā lokaiṣaṇobhe hyete eṣaṇe eva bhavatastasmādbrāhmaṇaḥ pāṇḍityaṃ nirvidya bālyena tiṣṭhāsedvālyaṃ ca pāṇḍityaṃ ca nirvidyātha muniramaunaṃ ca maunaṃ ca nirvidyātha brāhmaṇaḥ sa brāhmaṇaḥ kena syādyena syāttenedṛśa evāto'nyadārtaṃtato ha kaholaḥ kauṣītakeya upararāma

Then Kahola Kaushîtakeya asked. 'Yâgñavalkya, 'he said, 'tell me the Brahman which is visible, not invisible, the Self (Âtman), who is within all.'
Yâgñavalkya replied: 'This, thy Self, who is within all.'
'Which Self, O Yâgñavalkya, is within all?'
Yâgñavalkya replied: 'He who overcomes hunger and thirst, sorrow, passion, old age, and death. When Brâhmanas know that Self, and have risen above the desire for sons, wealth, and (new) worlds, they wander about as mendicants. For a desire for sons is desire for wealth, a desire for wealth is desire for worlds. Both these are indeed desires. Therefore let a Brâhmana, after he has done with learning, wish to stand by real strength; after he has done with that strength and learning, he becomes a Muni (a Yogin); and after he has done with what is not the knowledge of a Muni, and with what is the knowledge of a Muni, he is a Brâhmana. By whatever means he has become a Brâhmana, he is such indeed. Everything else is of evil.' After that Kahola Kaushîtakeya held his peace.

3.5.1.p1

iti tṛtīyādhyāye pañcamaṃ brāhmaṇam