ChU 7.21.1
यदा वै करोत्य् अथ निस्तिष्ठति । नाकृत्वा निस्तिष्ठति । कृत्वैव निस्तिष्ठति । कृतिस् त्व् एव विजिज्ञासितव्येति । कृतिं भगवो विजिज्ञास इति
yadā vai karoty atha nistiṣṭhati | nākṛtvā nistiṣṭhati | kṛtvaiva nistiṣṭhati | kṛtis tv eva vijijñāsitavyeti | kṛtiṃ bhagavo vijijñāsa iti
Devanagari rendered by HREEM from the edition's roman (IAST) text; the IAST is the edition's own.
'When one performs all sacred duties, then one attends really on a tutor. One who does not perform his duties, does not really attend on a tutor. Only he who performs his duties, attends on his tutor. This performance of duties, however, we must desire to understand.' 'Sir, I desire to understand it.'
Translated by F. Max Müller