Shatapatha Brahmana 11.8.3.3

11.8.3.3

atho apyāhuḥ aindrāgna evaiṣa paśuḥ syādityete vai devate anvantye devā yadyārto yajate pārayata eva yadi mahasāyajate pārayata eva tasmādaindrāgna evaiṣa paśuḥ syāditi

And they also say, 'To Indra and Agni that victim should belong; for behind these two deities are (all) the other gods;--if one who is afflicted sacrifices, those two (gods) sustain him; and if one sacrifices with (a desire for) abundance, they sustain him: therefore it is to Indra and Agni that this victim should belong.'