Śatapatha Brāhmaṇa ("of a hundred paths") 1.3.5.4

1.3.5.4

āgneyīranvāha | svayaivainametāddevatāyā samindhe gāyatrīranvāha gāyatraṃ vā agneścandaḥ svenaivainametacandasāsamindhe vīryaṃ gāyatrī brahma gāyatrī vīryeṇaivainametatsamindhe

He recites (verses) addressed to Agni: he accordingly kindles it (the fire) with the aid of its own deity. In the gâyatrî metre (are the verses which) he recites; for the gâyatrî is Agni's metre: by means of its own metre he thereby kindles it. The gâyatrî is vigour, the gâyatrî is the brahman (the priestly order): with vigour he thereby kindles it.