The reply of Lord Siva was the third chapter of the Upanishad.
I am the Brahman. I am the absolute bliss, absolute consciousness and the Supreme Being who is tranquillized, eternal and everlasting. ( "I " here does not denote Lord Siva alone, it is used in a wider sense of Chinmatra.
Lord Siva continues.
I have no Aham-hara. I have no "I" with me. I am devoid of anything. I am the ether of consciousness or Cit Akasa.
I am Turya only. (Turya is the fourth state of Atman beyond Jagrat or waking, Swapna or dreaming and Susupti or dreamless sleep).
I am the pure, absolute love, absolute knowledge and happiness. I am desire-less, disease-less, change-less and without any attachment.
I am imperishable and indivisible one essence. I am boundary-less. I have no limits and I am also the core of the core.
I am beyond the scope of Speech and mind. I am the Atman or self. I am the Paramatman or Supreme Self.
I have no beginning, means or end. I resemble ether and transcending ether and transcending all.
I am the residuum that ever remains.
I am devoid of body, feelings and other mental functions or material perceptions.
I am the inference. I am full. I am always content and satisfied.
I only appear as everything. Nothing is beyond me.
I support all the three worlds. I am served by Vedas and demonstrated by Sastras.
I am always fixed in Chitta meditating.
I am the absolute Brahman. I am non-dual and include everything.
I am the Adi-Sesa or prime residuum and Sesa or final residuum.
I have no name or form. I am beyond liberation and bondage.
It is I am who is beyond Turya,
I am the importance of Om. I do not exist and I am not non-existing which is beyond the scope of mind and speech.
Reference: Sanskrit Text Reference