CHĀNDOGYA UPANISHAD · 8.5.2

अथ यत् सत्त्रायणम् इत्य् आचक्षते ब्रह्मचर्यम् एव तत् ।
ब्रह्मचर्येण ह्य् एव सत आत्मनस् त्राणं विन्दते ।
अथ यन् मौनम् इत्य् आचक्षते ब्रह्मचर्यम् एव तत् ।
ब्रह्मचर्येण ह्य् एवात्मानम् अनुविद्य मनुते ॥

atha yat sattrāyaṇam ity ācakṣate brahmacaryam eva tat ।
brahmacaryeṇa hy eva sata ātmanas trāṇaṃ vindate ।
atha yan maunam ity ācakṣate brahmacaryam eva tat ।
brahmacaryeṇa hy evātmānam anuvidya manute ॥

What people call sacrifice (sattrâyana), that is really abstinence, for by abstinence he obtains from the Sat (the true), the safety (trâna) of the Self. What people call the vow of silence (mauna), that is really abstinence, for he who by abstinence has found out the Self, meditates (manute).

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