Śatapatha Brāhmaṇa ("of a hundred paths") 6.1.2.28

6.1.2.28

sa upadadhāti | tayā devatayeti vāgvai sā devatāṅgirasvaditi prāṇo vā aṅgirā dhruvā sīdeti sthirā sīdetyetadatho pratiṣṭhitā sīdeti vācā caivainametatprāṇena ca cinoti vāgvā agniḥ prāṇa indra aindrāgno 'gniryāvānagniryāvatyasya mātrā tāvataivainametaccinotīndrāgnī vai sarve devāḥ sarvadevatyo 'gniryāvānagniryāvatyasya mātrā tāvataivainametaccinoti

He builds up with, 'By that deity'--that deity, doubtless, is Vâk (speech),--'Aṅgiras-like,'--Aṅgiras, doubtless, is the breath;--'lie thou steady!'--that is, 'lie thou firm;' or 'lie thou firmly established.' It is both with speech and with breath that he builds; for Agni is speech, and Indra is the breath; and the fire (agni) relates to Indra and Agni: as great as Agni is, as great as is his measure, by so much he thus builds him up. And again, Indra and Agni are all the gods, (for) Agni belongs to all deities: thus as great as Agni is, as great as is his measure, by so much he thus builds him up.