Shatapatha Brahmana 3.4.2.2

3.4.2.2

te 'viduḥ | pāpīyāṃso vai bhavāmo 'surarakṣasāni vai no 'nuvyavāgurdviṣadbhyo vai radhyāmo hanta saṃjānāmahā ekasya śriyai tiṣṭhāmahā iti ta indrasya śriyā atiṣṭhanta tasmādāhurindraḥ sarvā devatā indraśreṣṭhā devā iti

They became aware of it,--'Forsooth, we are in an evil plight, the Asura-Rakshas have come in between us: we shall fall a prey to our enemies. Let us come to an agreement and yield to the excellence of one of us!' They yielded to the excellence of Indra; wherefore it is said, 'Indra is all the deities, the gods have Indra for their chief.'