BṚHADĀRAṆYAKA UPANISHAD · 4.3.1

जनकं ह वैदेहं याज्ञवल्क्यो जगाम ।
सम् एनेन वदिष्य इति ।
अथ ह यज् जनकश् च वैदेहो याज्ञवल्क्यश् चाग्निहोत्रे समूदाते ।
तस्मै ह याज्ञवल्क्यो वरं ददौ ।
स ह कामप्रश्नम् एव वव्रे ।
तं हास्मै ददौ ।
तं ह सम्राड् एव पूर्वः पप्रच्छ ॥

janakaṃ ha vaidehaṃ yājñavalkyo jagāma ।
sam enena vadiṣya iti ।
atha ha yaj janakaś ca vaideho yājñavalkyaś cāgnihotre samūdāte ।
tasmai ha yājñavalkyo varaṃ dadau ।
sa ha kāmapraśnam eva vavre ।
taṃ hāsmai dadau ।
taṃ ha samrāḍ eva pūrvaḥ papraccha ॥

Yâgñavalkya came to Ganaka Vaideha, and he did not mean to speak with him. But when formerly Ganaka Vaideha and Yâgñavalkya had a disputation on the Agnihotra, Yâgñavalkya had granted him a boon, and he chose (for a boon) that he might be free to ask him any question he liked. Yâgñavalkya granted it, and thus the King was the first to ask him a question.

F. Max Müller · The Upanishads, Sacred Books of the East 15 (1884)