CHĀNDOGYA UPANISHAD · 8.5.1

अथ यद् यज्ञ इत्य् आचक्षते ब्रह्मचर्यम् एव तत् ।
ब्रह्मचर्येण ह्य् एव यो ज्ञाता तं विन्दते ।
अथ यद् इष्टम् इत्य् आचक्षते ब्रह्मचर्यम् एव तत् ।
ब्रह्मचर्येण ह्य् एवेष्ट्वात्मानम् अनुविन्दते ॥

atha yad yajña ity ācakṣate brahmacaryam eva tat ।
brahmacaryeṇa hy eva yo jñātā taṃ vindate ।
atha yad iṣṭam ity ācakṣate brahmacaryam eva tat ।
brahmacaryeṇa hy eveṣṭvātmānam anuvindate ॥

What people call sacrifice (yagña), that is really abstinence (brahmakarya). For he who knows, obtains that (world of Brahman, which others obtain by sacrifice), by means of abstinence. What people call sacrifice (ishta), that is really abstinence, for by abstinence, having searched (ishtvâ), he obtains the Self.

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