Brihadaranyaka Upanishad 6.2.3-3

6.2.3-3

athainaṃ vasatyopamantrayāṃ cakre'nādṛtya vasatiṃ kumāraḥ pradudrāva sa ājagāma pitaraṃ tam̐ hovāceti vāva kila no bhavānpurānuśiṣṭānavoca iti katham̐ sumedha iti pañca mā praśnānrājanyabandhuraprākṣīttato naikaṃcana vedeti katame ta itīma iti ha pratīkānyudājahāra

Then the King invited him to stay. The boy, disregarding the invitation to stay, hurried away. He came to his father and said to him, 'Well, did you not tell me before that you had (fully) instructed me?' 'What has hurt you, my sagacious child?' 'That wretch of a Kshatriya asked me five questions, and I knew not one of them.' 'Which are they?' 'These,' and he quoted their first words.