Question: what do the upanishads contain?
Answer: The Upanishads contain four sentences, the Mahāvākyas (Great Sayings), which were used by Shankara to establish the identity of Atman and Brahman as scriptural truth: "Prajñānam brahma" - "Consciousness is Brahman" (Aitareya Upanishad) "Aham brahmāsmi" - "I am Brahman" (Brihadaranyaka Upanishad)