Śatapatha Brāhmaṇa ("of a hundred paths") 1.7.4.20

1.7.4.20

sa vai vācaṃyama eva syāt | brahmanprasthāsyāmītyaitasmādvacaso vivṛhanti vā ete yajṇaṃ kṣaṇvanti ye madhye yajñasya pākayajñiyayeḍayā caranti brahmā vā ṛtvijām bhiṣaktamastadbrahmā saṃdadhāti na ha saṃdadhyādyadvāvadyamāna āsīta tasmādvācaṃyama eva syāt

If he should utter any human sound before that time, let him there and then mutter some Rik or Yagus-text addressed to Vishnu; for Vishnu is the sacrifice, so that he thereby again obtains a hold on the sacrifice: and this is the expiation of that (breach of silence).