CHĀNDOGYA UPANISHAD · 3.17.1
स यद् अशिशिषति यत् पिपासति यन् न रमते ता अस्य दीक्षाः ॥
sa yad aśiśiṣati yat pipāsati yan na ramate tā asya dīkṣāḥ ॥
When a man (who is the sacrificer) hungers, thirsts, and abstains from pleasures, that is the Dîkshâ (initiatory rite).
F. Max Müller · The Upanishads, Sacred Books of the East 1 (1879)