CHĀNDOGYA UPANISHAD · 4.16.1

एष ह वै यज्ञो यो ऽयं पवते ।
एष ह यन्न् इदं सर्वं पुनाति ।
यद् एष यन्न् इदं सर्वं पुनाति ।
तस्माद् एष एव यज्ञः ।
तस्य मनश् च वाक् च वर्तनी ॥

eṣa ha vai yajño yo ’yaṃ pavate ।
eṣa ha yann idaṃ sarvaṃ punāti ।
yad eṣa yann idaṃ sarvaṃ punāti ।
tasmād eṣa eva yajñaḥ ।
tasya manaś ca vāk ca vartanī ॥

Verily, he who purifies (Vâyu) is the sacrifice, for he (the air) moving along purifies everything. Because moving along he purifies everything, therefore he is the sacrifice. Of that sacrifice there are two ways, by mind and by speech.

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