Śatapatha Brāhmaṇa ("of a hundred paths") 8.6.3.5

8.6.3.5

yadveva gārhapatyamupadadhāti | annaṃ vai gārhapatyo 'ttāyamagniścito 'ttra evaitadannamapidadhāti madhyato madhyata evāsminnetadannaṃ dadhāti

And, again, as to why he lays down the Gârhapatya. The Gârhapatya, doubtless, is food, and this built Agni is an eater: it is to the eater he thus offers that food;--in the centre (he lays down the Gârhapatya): in the very middle (of the body) he thus lays food into him.