One of the most famous Upanishads is the Kena Upanishad, aka the Talavakara Brahmana Upanishad. It gets its name because it begins with the word Kena meaning "by whom"; its first verse consists of a shishya asking his guru "At whose wish does the mind sent forth proceed on its errand? At whose command does the first breath go forth? At whose wish do we utter this speech? What god directs the eye, or the ear?" And then the rest of the Upanishad consists of the guru's response.
But my question is about the identities of the guru and the shishya. The Dvaita philosopher Madhvacharya claims that the guru is Brahma and thathe is teaching Shiva. In this excerpt from his commentary on the Kena Upanishad, Madhvacharya gives a quote from a work he calls the "Brahmasara":
Brahma, the four-faced, was seated alone in his heaven called Vaijayanta, when Sadashiva approaching him, asked the following questions, in order to know the truth about Vishnu :— "The mind thinks of objects (desirable and undesirable) not under the control of the human soul (Purusha).... By whom sent, therefore, the mind goes to its object; by whose command does similarly the chief Prana the best of all function? What divinity controls and directs to their proper objects, eyes, ears speech and the rest?"
Being thus asked Brahma first meditated on the Lord Narayana, who is the support of all, who is the incomparable, the omniscient, the omnipotent, and free of all imperfections and then replied to the Lord of Uma:— "He who is the controller and regulator of Prana, of all senses like the eye, etc., is not fully comprehensible by even all the devas, because he is all-full. He is the leader of Breath (Prana) and the rest, He knows everything in all time. He is the best of all, he is present everywhere, he is the best of everything. He is Vishnu, know him as such."
In fact Madhvacharya frames almost his entire commentary on the Kena Upanishad as an extended quotation from this Brahmasara work. Now as I discuss here, Madhvacharya's scriptural references are notoriously hard to track down, and this is no exception; we don't have an extant copy of the Brahmasara, and as far as I know there's no reference to such a work before the time of Madhvacharya.
So my question is, what other scriptures mention that the Kena Upanishad is a dialogue between Brahma and Shiva? Is this mentioned in the Puranas? I know Adi Sankaracharya doesn't identify the guru and ahishya in his commentary, but are there any other commentators who do?
By the way, this isn't the only case where Madhvacharya makes a peculiar claim about the origin of an Upanishad; he says something similar about the Mandukya Upanishad as I discuss here.
