Śatapatha Brāhmaṇa ("of a hundred paths") 2.3.4.40

2.3.4.40

athāgneyī | tadagnaya evaitadātmānamantataḥ paridadāti guptyai pari te dūḍabho ratho 'smān aśnotu viśvataḥ yena rakṣasi dāśuṣa iti yajamānā vai dāśvāṃso yo ha vā asyānādhṛṣyatamo rathastenaiṣa yajamānānabhirakṣati sa yaste 'nādhṛṣyatamo ratho yena yajamānānabhirakṣasi tena naḥ sarvato 'bhigopāyetyevaitadāha triretajjapati

Thereupon a verse to Agni (Vâg. S. III, 36),--whereby he finally makes himself over to Agni for protection: 'May thine unapproachable chariot, wherewith thou protectest the worshippers, encircle us on every side!' The worshippers, doubtless, are the sacrificers; and what unassailable chariot he (Agni) possesses, therewith he protects the sacrificers. Hence he thereby means to say, 'what unassailable chariot thou possessest, wherewith thou protectest the sacrificers, therewith do thou guard us on every side.' This (verse) he mutters thrice.