Which Upanishads are quoted in sage Vyasa’s Brahma Sutras?
The Badarayana-Vyasa Brahma Sutras are a compilation of extremely terse Sutras. These Sutras are impossible to understand without the commentary attached to them. There is no direct quote from any Upanishad in any of these Sutras. These Sutras are often not even complete sentences. It is the commentaries that claim that the Sutras are talking about particular shlokas from specific Upanishads. The Upanishads quoted by Sri Sankaracharya to explain the various Sutras are Aitereya, Brhadaranyaka, Chandogya, Isavasya, Jabala, Katha, Kausitaki, Kena, Mandukya, Mundaka, Prasna, Svetasvatara and Tattiriya, a total of 13. The Upanishads quoted by Sri Ramanuja to explain the Sutras are Aitereya, Brhadaranyaka, Chandogya, Isavasya, Katha, Kausitaki, Kena, Mahanarayana, Mundaka, Mudgala, Prasna, Subala, Svetasvara and Taittiriya, a total of 14.
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