Śatapatha Brāhmaṇa ("of a hundred paths") 3.8.1.6

3.8.1.6

athāha paryagnaye 'nubrūhīti | ulmukamādāyāgnītparyagniṃ karoti tadyatparyagniṃ karotyacidramevainametadagninā parigṛhṇāti nedenaṃ nāṣṭrā rakṣāṃsi pramṛśānityagnirhi rakṣasāmapahantā tasmātparyagniṃ karoti tadyatrainaṃ śrapayanti tadabhipariharati

Thereupon he says (to the Hotri), 'Recite to Agni circumambient!' Having taken a firebrand, the Agnîdh carries the fire round (the victim). Why he carries the fire round, is that he encircles it (the victim) by means of the fire with an unbroken fence, lest the evil spirits should seize upon it; for Agni is the repeller of the Rakshas; therefore he carries the fire round. He carries it round the place where they cook it (the victim).