Śatapatha Brāhmaṇa ("of a hundred paths") 2.1.4.10

2.1.4.10

tadāhuḥ | yannarcā na sāmnā na yajuṣāgnirādhīyate 'tha kenādhīyata iti brahmaṇo haivaiṣa brahmaṇādhīyate vāgvai brahma tasyai vācaḥ satyameva brahma tā vā etāḥ satyameva vyāhṛtayo bhavanti tadasya satyenaivādhīyate

Here now they say, 'If the fire is not setup with either a rik-verse, or a sâman, or a yagus, wherewith then is it set up?' Verily, that (fire) is of the brahman: with the brahman it is set up. The brahman is speech: of that speech it is. The brahman is the truth, and the truth consists in those same (three) mystic utterances: hence his (fire) is established by means of the truth.