Śatapatha Brāhmaṇa ("of a hundred paths") 1.7.4.19

1.7.4.19

athāsmai brahmabhāgam paryāharanti | brahmā vai yajñasya dakṣiṇata āste 'bhigoptā sa etam bhāgam pratividāna āste yatprāśitraṃ tadasmai paryāhārṣustatprāśīdatha yamasmai brahmabhāgam paryāharanti tena bhāgī sa yadata ūrdhvamasaṃsthitaṃ yajñasya tadabhigopāyati tasmādvā asmai brahmabhāgam paryāharanti

He (the Brahman) must maintain silence (from the time he takes his seat on being elected) up to that speech (of the Adhvaryu), 'Brahman, shall I step forward?' Those (priests) who, in the midst of the sacrifice, perform the idâ, which represents the domestic offerings (pâkayagña), tear the sacrifice to pieces, injure it. Now the Brahman, assuredly, is the best physician: hence the Brahman thereby restores the sacrifice; but, if he were to sit there talking, he would not restore it: he must therefore maintain silence.