Śatapatha Brāhmaṇa ("of a hundred paths") 1.5.3.22

1.5.3.22

ta uttame prayāje | svāhākāreṇaiva sarvaṃ yajñaṃ samasthāpayantsvāhāgnimiti tadāgneyamājyabhāgaṃ samasthāpayantsvāhā somamiti tatsaumyamājyabhāgaṃ samasthāpayantsvāhāgnimiti tadya eṣa ubhayatrācyuta āgneyaḥ puroḍāśo bhavati taṃ samasthāpayan

At the last fore-offering they established the entire sacrifice by means of the Svâhâ ('hail!'). With 'Svâhâ Agni!' they established the butter-portion for Agni; with 'Svâhâ Soma!' they established the butter-portion for Soma; and with (the second) 'Svâhâ Agni!' they established that indispensable sacrificial cake which there is on both occasions (i.e. at the new- and full-moon sacrifices).