Śatapatha Brāhmaṇa ("of a hundred paths") 1.6.3.20

1.6.3.20

sa hāgniruvāca | mayyeva vaḥ sarvebhyo juhvatu tadvo 'haṃ mayyābhajāmīti tasmādagnau sarvebhyo devebhyo juhvati tasmādāhuragniḥ sarvā devatā iti

Agni then said, 'In me they shall sacrifice for all of you, and thus I give you a share in me!' For this reason they sacrifice in Agni (the fire) to all the gods; and for this reason they say that Agni is all the deities.