Shatapatha Brahmana 1.6.1.15

1.6.1.15

sa yadyenam purastāt | asurarakṣasānyāsisaṃkṣantyāgnereva tānyapahanti rakṣohā rakṣasāmapahantā yadi madhyata asurarakṣasānyāsisaṃkṣantyagnireva tānyapahanti rakṣohā rakṣasāmapahantā yadi paścādasurarakṣasānyāsisaṃkṣantyagnireva tānyapahanti rakṣohā rakṣasāmapahantā sa evaṃ sarvato 'gnibhirgupyamānaḥ svargaṃ lokaṃ samaśnute

And if the Asuras and Rakshas try to attack him (the sacrificer) in front, Agni repels them, as the Rakshas-killer, the Repeller of the Rakshas: if they try to attack him in the centre, Agni repels them, as the Rakshas-killer, the repeller of the Rakshas; and if they try to attack him from behind, Agni repels them, as the Rakshas-killer, the repeller of the Rakshas: being thus guarded on every side by Agnis, he gains the world of heaven.