Shatapatha Brahmana 3.8.1.9

3.8.1.9

atholmukamādāyāgnītpurastātpratipadyate | agnimevaitatpurastātkarotyagniḥ purastānnāṣṭrā rakṣāṃsyapaghnannetyathābhayenānāṣṭreṇa paśuṃ nayanti taṃ vapāśrapaṇībhyām pratiprasthātānvārabhate pratiprasthātāramadhvaryuradhvaryuṃ yajamānaḥ

Thereupon the Agnîdh, taking a (new) firebrand, walks in front: whereby he places Agni in front, thinking, 'Agni shall repel the evil spirits in front!' and they lead the victim after him (to the slaughtering-place) on a (way) free from danger and injury. The Pratiprasthâtri holds on to it from behind by means of the two spits, and the Adhvaryu (holds on to) the Pratiprasthâtri, and the Sacrificer to the Adhvaryu.