Shatapatha Brahmana 10.5.1.1

10.5.1.1

tasya vā etasyāgneḥ vāgevopaniṣadvācā hi cīyata ṛcā yajuṣā sāmneti nu daivyātha yanmānuṣyā vācāhetīdaṃ kurutetīdaṃ kuruteti tadu ha tayā cīyate

The mystic import of this Fire-altar, doubtless, is Speech; for it is with speech that it is built: with the Rik, the Yagus and the Sâman as the divine (speech); and when he (the Adhvaryu) speaks with human speech, 'Do ye this! do ye that!' then also it (the altar) is built therewith.