Shatapatha Brahmana 3.5.2.2

3.5.2.2

athodyacantīdhmam | upayacantyupayamanīrathāhāgnaye prahriyamāṇāyānubrūhyekasphyayānūdehītyanūdaiti pratiprasthātaikasphyayaitasmānmadhyamācaṅkorya eṣa vederjaghanārdhe bhavati tadyadevātrāntaḥpātena gārhapatyasya vedervyavacinnam bhavati tadevaitadanusaṃtanoti

They lift the (burning) fire-wood, and place it on the underlayer. Thereupon he says (to the Hotri), 'Recite for Agni as he is taken forward!' (and to the Pratiprasthâtri), 'Come up after me with the single sword(-line)!' The Pratiprasthâtri goes up after him with the single sword(-line) as far as that middle peg on the hind-part of the altar: whatever part of the Gârhapatya is cut off from the altar by that intermediate (peg), that he thereby carries on to (connects with) it.