Śatapatha Brāhmaṇa ("of a hundred paths") 6.6.2.7

6.6.2.7

dvābhyām pravṛṇakti | dvipādyajamāno yajamāno 'gniryāvānagniryāvatyasya mātrā tāvataivaināmetatpravṛṇakti gāyatryā ca triṣṭubhā ca prāṇo gāyatryātmā triṣṭubetāvānvai paśuryāvānprāṇaścātmā ca tadyāvānpaśustāvataivaināmetatpravṛṇaktyatho agnirvai gāyatrīndrastriṣṭubaindrāgno 'gniryāvānagniryāvatyasya mātrā tāvataivaināmetatpravṛṇaktīndrāgnī vai sarve devāḥ sarvadevatyo 'gniryāvānagniryāvatyasya mātrā tāvataivaināmetatpravṛṇakti tayoḥ sapta padāni saptacitiko gniḥ sapta 'rtavaḥ saṃvatsaraḥ saṃvatsaro 'gniryāvānagniryāvatyasya mātrā tāvattadbhavati

With two (verses) he heats it on the fire,--the Sacrificer is two-footed, and the Sacrificer is Agni: as great as Agni is, as great as is his measure, by so much he thus heats it (the pan). [He does so] with a gâyatrî and a trishtubh verse,--the Gâyatrî is the vital air, and the Trishtubh the body; and the animal is as much as the vital air and the body: thus by as much as the animal (consists of) he puts that (pan) on the fire. And, again, the Gâyatrî is Agni, and the Trishtubh is Indra; and the fire relates to Indra and Agni: as great as the fire is, as great as is its measure, by so much he thus heats it. These two (verses) have seven feet (viz. three and four respectively),--the fire-altar consists of seven layers; seven seasons are a year, and Agni is the year: as great as Agni is, as great as is his measure, so great does this become.