Chandogya Upanishad
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.
tayor anyatarāṃ manasā saṃskaroti brahmā vācā hotādhvaryur udgātānyatarām sa yatropākṛte prātaranuvāke purā paridhānīyāyā brahmā vyavavadati
The Brahman priest performs one of them in his mind, the Hotri, Adhvaryu, and Udgâtri priests perform the other by words. When the Brahman priest, after the Prâtaranuvâka ceremony has begun, but before the recitation of the Paridhânîyâ hymn, has (to break his silence and) to speak,
anyatarām eva vartanīṃ saṃskaroti hīyate 'nyatarā sa yathaikapād vrajan ratho vaikena cakreṇa vartamāno riṣyaty evam asya yajño riṣyati yajñaṃ riṣyantaṃ yajamāno 'nu riṣyati sa iṣṭvā pāpīyān bhavati
He performs perfectly the one way only (that by words), but the other is injured. As a man walking on one foot, or a carriage going on one wheel, is injured, his sacrifice is injured, and with the injured sacrifice the sacrificer is injured; yes, having sacrificed, he becomes worse.
atha yatra upākṛte prātaranuvāke na purā paridhānīyāyā brahmā vyavavadaty ubhe eva vartanī saṃskurvanti na hīyate 'nyatarā
But when after the Prâtaranuvâka ceremony has begun and before the recitation of the Paridhânlyâ hymn, the Brahman priest has not (to break his silence and) to speak, they perform both ways perfectly, and neither of them is injured.
sa yathobhayapād vrajan ratho vobhābhyāṃ cakrābhyāṃ vartamānaḥ pratitiṣṭhaty evam asya yajñaḥ pratitiṣṭhati yajñaṃ pratitiṣṭhantaṃ yajamāno 'nu pratitiṣṭhati sa iṣṭvā śreyān bhavati
As a man walking on two legs and a carriage going on two wheels gets on, so his sacrifice gets on, and with the successful sacrifice the sacrificer gets on; yes, having sacrificed, he becomes better.