Śatapatha Brāhmaṇa ("of a hundred paths") 7.4.1.41

7.4.1.41

sa kārṣmaryamayīṃ dakṣiṇata upadadhāti | agneṣṭvā tejasā sādayāmīti yadevāsya tadagnisteja ādāya dakṣiṇākarṣattadasminnetatpratidadhātyagnirmūrdhā divaḥ kakudityeṣa u so 'gnirgāyatryā gāyatro 'gniryāvānagniryāvatyasya mātrā tāvataivaināmetadupadadhāti ghṛtena pūrṇā bhavatyāgneyaṃ vai ghṛtaṃ svenaivainametadbhāgena svena ramena prīṇāti

The kârshmarya one he lays down on the right side, with (Vâg. S. XIII, 13), 'By Agni's fiery spirit I settle thee!'--that fiery spirit of his (Pragâpati's) which Agni then took and carried off to the south, he now puts back into him.--'Agni, the head, the summit of the sky, he, the lord of the earth, animates the seeds of the waters,' for Agni indeed is this (spoon). With a Gâyatrî verse (he performs),--Agni is Gâyatra: as great as Agni is, as great as is his measure, with so much he thus lays down that (spoon). It is filled with ghee, for ghee belongs to Agni: with his own share, with his own life-sap he thus gratifies him.