Bṛhadāraṇyaka Upaniṣad ("Great Forest Teaching") 3.1.2

3.1.2

tānhovāca brāhmaṇā bhagavanto yo vo brahmiṣṭhaḥ sa etā gā udajatāmiti | te ha brāhmaṇā na dadhṛṣuratha ha yājñavalkyaḥ svameva brahmacāriṇamuvācaitāḥ somyodaja sāmaśravā3 iti tā hodācakāra te ha brāhmaṇāścukrudhuḥ kathaṃ no brahmiṣṭho bruvītetyatha ha janakasya vaidehasya hotāśvalo babhūva sa hainaṃ papraccha tvaṃ nu khalu no yājñavalkya brahmiṣṭhosī3 iti sa hovāca namo vayaṃ brahmiṣṭhāya kurmo gokāmā eva vayam̐ sma iti tam̐ ha tata eva praṣṭuṃ dadhre hotāśvalaḥ

And Ganaka spoke to them: 'Ye venerable Brâhmanas, he who among you is the wisest, let him drive away these cows.'
Then those Brâhmanas durst not, but Yâgñavalkya said to his pupil: 'Drive them away, my dear.'
He replied: 'O glory of the Sâman ' and drove them away.
The Brâhmanas became angry and said: 'How could he call himself the wisest among us?'
Now there was Asvala, the Hotri priest of Ganaka Vaideha. He asked him: 'Are you indeed the wisest among us, O Yâgñavalkya?' He replied: 'I bow before the wisest (the best knower of Brahman), but I wish indeed to have these cows.'
Then Asvala, the Hotri priest, undertook to question him.