CHĀNDOGYA UPANISHAD · 7.20.1

यदा वै निस्तिष्ठत्य् अथ श्रद्दधाति ।
नानिस्तिष्ठञ् छ्रद्दधाति ।
निस्तिष्ठन्न् एव श्रद्दधाति ।
निष्ठा त्व् एव विजिज्ञासितव्येति ।
निष्ठां भगवो विजिज्ञास इति ॥

yadā vai nistiṣṭhaty atha śraddadhāti ।
nānistiṣṭhañ chraddadhāti ।
nistiṣṭhann eva śraddadhāti ।
niṣṭhā tv eva vijijñāsitavyeti ।
niṣṭhāṃ bhagavo vijijñāsa iti ॥

'When one attends on a tutor (spiritual guide), then one believes. One who does not attend on a tutor, does not believe. Only he who attends, believes. This attention on a tutor, however, we must desire to understand.' 'Sir, I desire to understand it.'

F. Max Müller · The Upanishads, Sacred Books of the East 1 (1879)