Is there any refutation of the idea that Indra is Brahman?
Yes, the Vedas do, and the Brahma sutras make this matter more clear.
The Upanishad passage in question is here:
Indra said: 'I am prâna, meditate on me as the conscious self (pragñâtman), as life, as immortality. Life is prâna, prâna is life. Immortality is prâna, prâna is immortality. As long as prâna dwells in this body, so long surely there is life. By prâna he obtains immortality in the other world, by knowledge true conception. He who meditates on me as life and immortality, gains his full life in this world, and obtains in the Svarga world immortality and indestructibility.'
Then the question arises as to what the words Prana and Indra in this passage mean. Ramanujacharya says the following in his commentary on Brahma Sutra 1.1.29:
Here the doubt arises whether the being called Prâna and Indra, and designating itself as the object of a meditation most beneficial to man, is an individual soul, or the highest Self.
An individual soul, the Pûrvapakshin maintains. For, he says, the word 'Indra' is known to denote an individual God.
This view is rejected by the Sûtra. The being called Indra and Prâna is not a mere individual soul, but the highest Brahman, which is other than all individual souls.
So, this sutra says the word "Indra" denotes the supreme Brahman in the passage.
However, now the question is, is Indra the Devata really Brahman? Or is it the Antaryami (inner-soul) of Indra who is Brahman? This question is referenced in Ramanujacharya's commentary on the next sutra:
But how then can Indra, who is known to be an individual person only, enjoin meditation on himself?--To this question the next Sûtra replies.
The sutra is:
- The instruction (given by Indra about himself) (is possible) through insight based on Scripture, as in the case of Vâmadeva.
And Ramanujacharya's commentary:
From these and similar texts Indra has learned that the highest Self has the indiviual souls for its body, and that hence words such as 'I' and 'thou,' which denote individual beings, extend in their connotation up to the highest Self; when, therefore, he says, 'Know me only', and 'Meditate on me', he really means to teach that the highest Self [Brahman], of which his own individual person is the body, is the proper object of meditation. 'As in the case of Vâmadeva.' As the Rishi Vâmadeva perceiving that Brahman is the inner Self of all, that all things constitute its body, and that the meaning of words denoting a body extends up to the principle embodied, denotes with the word 'I' the highest Brahman to which he himself stands in the relation of a body, and then predicates of this 'I' Manu Sûrya and other beings--'Seeing this the Rishi. Vâmadeva understood, I am Manu, I am Sûrya' (Bri. Up. I, 4, 10). Similarly Prahlâda says, 'As the Infinite one abides within all, he constitutes my "I" also; all is from me, I am all, within me is all.' (Vi. Pu. I, 19, 85.)
Hence, Indra Devata is not the supreme Brahman, otherwise this sutra would not exist.
Even Shankaracharya says the same thing:
We therefore arrive at the conclusion that, on account of the multitude of references to the interior Self, the chapter contains information regarding Brahman, not regarding the Self of some deity.--How then can the circumstance of the speaker (Indra) referring to himself be explained?