Shatapatha Brahmana 6.5.1.12

6.5.1.12

tribhiḥ prayauti | trivṛdagniryāvānagniryāvatyasya mātrā tāvataivainametatprayauti dvābhyāṃ saṃsṛjati tatpañca pañcacitiko 'gniḥ pañca 'rtavaḥ saṃvatsaraḥ saṃvatsaro 'gniryāvānagniryāvatyasya mātrā tāvattadbhavati tribhirapa upasṛjati tadaṣṭāvaṣṭākṣarā gāyatrī gāyatro 'gniryāvānagniryāvatyasya mātrā tāvattadbhavatyatho aṣṭākṣarā vā iyamagre 'sṛjyata tadyāvatīyamagre 'sṛjyata tāvatīmevaināmetatkaroti

With three (formulas) he kneads (the clay),--threefold is Agni: as great as Agni is, as great as is his measure, with so much he thus kneads him. With two (verses) he mixes,--that makes five;--of five layers consists the fire-altar (Agni); five seasons are a year, and the year is Agni: as great as Agni is, as great as is his measure, so great does this become. With three (formulas) he pours water thereto,--that makes eight;--of eight syllables the Gâyatrî metre consists, and Agni is Gâyatra: as great as Agni is, as great as is his measure, so great does this become. And, moreover, as one of eight syllables this (earth) was created in the beginning: thus as great as this (earth) was created in the beginning, so great he thus makes this (fire-pan representing the earth).