Shatapatha Brahmana 11.6.2.5

11.6.2.5

te hocuḥ ati vai no'yaṃ rājanyabandhuravādīddhantainam brahmodyamāhvayāmahā iti sa hovāca yājñavalkyo brāhmaṇā vai vayaṃ smo rājanyabandhurasau yadyamuṃ vayaṃ jayema kamajaiṣmeti brūyāmātha yadyasāvasmānjayedbrāhmaṇānrājanyabandhurajaiṣīditi no brūyurmedamādṛḍhvamiti taddhāsya jajñuratha ha yājñavalkyo rathamāstāyānupradhāvayāṃ cakāra taṃ hānvājagāma sa hovācāgnihotraṃ yājñavalkya veditū3mityagnihotraṃ samrāḍiti

They said, 'Surely, this fellow of a Râganya has outtalked us: come, let us challenge him to a theological disputation!' Yâgñavalkya said, 'We are Brâhmanas, and he is a Râganya: if we were to vanquish him, whom should we say we had vanquished? But if he were to vanquish us, people would say of us that a Râganya had vanquished Brâhmanas: do not think of this!' They approved of his words. But Yâgñavalkya, mounting his car, drove after (the king). He overtook him, and he (the king) said, 'Is it to know the Agnihotra, Yâgñavalkya?'--'The Agnihotra, O king!' he replied.