Śatapatha Brāhmaṇa ("of a hundred paths") 4.6.7.6

4.6.7.6

te devā vācamabruvan | prācī prehīdam prajñapayeti sā hovāca kim me tataḥ syāditi yatkiṃ cāvaṣaṭkṛtaṃ svāhākāreṇa yajñe hūyate tatta iti tasmādyatkiṃ cāvaṣaṭkṛtaṃ svāhākāreṇa yajñe hūyate tadvācaḥ sā prācī praitsaitatprājñapayaditīdaṃ kurutetīdaṃ kuruteti

The gods said to Speech, 'Go thou forward and make this known!' She said, 'What will be my reward then?'--'Whatever in the sacrifice is offered with Svâhâ, and without Vashat, that shall be thine!' Hence whatever in the sacrifice is offered with Svâhâ, and without Vashat, that belongs to Speech. She then went forward and made that known, saying, 'Do this so! do this so!'