Katha Upanishad - Verse 1.2.9
Text: नैषा तर्केण मतिरापनेया प्रोक्तान्येनैव सुज्ञानाय प्रेष्ठ । यान्त्वमापः सत्यधृतिर्बतासि त्वादृङ्नो भूयान्नचिकेतः प्रष्टा ॥ ९ ॥ naiṣā tarkeṇa matirāpaneyā proktānyenaiva sujñānāya preṣṭha | yāntvamāpaḥ satyadhṛtirbatāsi tvādṛṅno bhūyānnaciketaḥ praṣṭā || 9 || 9. This idea cannot be reached by mere reasoning. This idea, Oh dearest, leads to sound knowledge, only if taught by another; thou hast reached it; Oh, thou art fixed in truth. May we find, Oh Nachiketas, a questioner like thee!...