Shatapatha Brahmana 8.3.1.11

8.3.1.11

atha diśyā upadadhāti | diśo vai diśyā diśa evaitadupadadhāti tadyābhirado vāyurdigbhiranantarhitābhirupaittā etāstā evaitadupadadhāti tā u evāmūḥ purastāddarbhastambaṃ ca logeṣṭakāścopadadhātyasau vā āditya etā amuṃ tadādityaṃ dikṣvadhyūhati dikṣu cinoti tā yattatraiva syurbahirdhā tatsyurbahirdho vā etadyoneragnikarma yatpurā puṣkaraparṇāttā yadihāhṛtyopadadhāti tadenā yonau puṣkaraparṇe pratiṣṭhāpayati tatho haitā abahirdhā bhavanti tā anantarhitāḥ svayamātṛṇāyā upadadhātyantarikṣaṃ vai madhyamā svayamātṛṇānantarhitāstadantarikṣāddiśo dadhātyuttarā uttarāstadantarikṣāddiśo dadhāti retaḥsicorvelayeme vai retaḥsicāvanayostaddiśo dadhāti tasmādanayordiśaḥ sarvata upadadhāti sarvatastaddiśo dadhāti tasmātsarvato diśaḥ samīcīḥ sarvatastatsamīcīrdiśo dadhāti tasmātsarvataḥ samīcyo diśaḥ

They said to Indra and Agni, 'Lay ye down for us this third layer!'--'What will accrue unto us therefrom? Ye two shall be the best of us!'--'So be it!' Accordingly Indra and Agni laid down for them that third layer; and hence people say, 'Indra and Agni are the best of gods.'