Shatapatha Brahmana 1.6.1.14

1.6.1.14

sa yadāgneyamājyabhāgaṃ yajati | agnimevaitatpurastātkurute rakṣohaṇaṃ rakṣasāmapahantāramatha yadāgneyaḥ puroḍāṣo bhavatyagnimevaitanmadhyataḥ kurute rakṣohaṇaṃ rakṣasāmapahantāramatha yadagniṃ sviṣṭakṛtaṃ yajatyagnimevaitatpaścātkurute rakṣohaṇaṃ rakṣasāmapahantāraṃ

Now when he pronounces the offering-prayer over Agni's butter-portion, he thereby places Agni in front, as the Rakshas-killer, the repeller of the Rakshas; and when Agni's sacrificial cake is (offered), he thereby places Agni in the midst, as the Rakshas-killer, the repeller of the Rakshas; and when he pronounces the offering-prayer to Agni Svishtakrit (the maker of good offering), he thereby places Agni in the rear, as the Rakshas-killer, the repeller of the Rakshas.