Śatapatha Brāhmaṇa ("of a hundred paths") 3.5.1.31

3.5.1.31

atha harati | yatra harati tadagnīdupasīdati sa vā agnīnāmeva nāmāni gṛhṇanharati yānvā amūndevā agre 'gnīnhotrāya prāvṛṇata te prādhanvaṃsta imā eva pṛthivīrupāsarpannimāmahaiva dve asyāḥ pare tenaivaitānnidānena harati

He then flings (the wooden sword); at the place where he flings, the Agnîdh sits. He flings while mentioning the names of the Agnis. For those (three) Agnis whom the gods at first chose for the office of Hotri passed away: they crept into these very earths,--namely, into this one and the two beyond it. It is really with this one that he now flings.