Śatapatha Brāhmaṇa ("of a hundred paths") 1.4.5.4

1.4.5.4

agne verhotraṃ verdūtyamiti | ubhayaṃ vā etadagnirdevānāṃ hotā ca dūtaśca tadubhayaṃ viddhi yaddevānāmasītyevaitadāhāvatāṃ tvāṃ dyāvāpṛthivī ava tvaṃ dyāvāpṛthivī iti nātra tirohitamivāsti sviṣṭakṛddevebhya indra ājyena haviṣābhūtsvāhetīndro vai yajñasya devatā tasmādāhendra ājyeneti vāce vā etamāghāramāghārayatīndro vāgityu vā āhustasmādvevāhendra ājyeneti

Further (Vâg. S. II, 9): 'O Agni, take thou upon thyself the office of Hotri, take thou upon thyself the part of messenger!' for Agni is both Hotri and messenger to the gods: hence he thereby says, 'know thou both (offices) which thou art (holding) for the gods!'--'May earth and heaven guard thee! Guard thou earth and heaven!' there is nothing obscure in this.--'Indra, by this butter-oblation, may be the maker of good offering (svishtakrit) for the gods! Svâhâ!' Indra, indeed, is the deity of sacrifice; therefore he says 'Indra, by this butter-oblation... 'It is for speech that he makes this sprinkling, and Indra is speech' so say some; and for this reason also he says Indra, by this butter-oblation...'