Brihadaranyaka Upanishad

He is never heard, but is the Hearer; He is never thought of, but is the Thinker; He is never known but is the Knower. There is no other seer than He, there is no other hearer than He, there is no other thinker than He, there is no other knower than He. He is your Self, the Inner Controller, the Immortal. Everything else but Him is perishable.”He is never seen, but is the Seer;