Katha Upanishad

 

“I will tell you briefly of that Goal which all the Vedas with one voice propound, which all the austerities speak of, and wishing for Which people practice discipline: It is Om.” “Om is the Supreme Brahman.” “God is the Syllable Om.” “Om is Brahman, the Primeval Being.” “That [Om] is the quintessence of the essences, the Supreme, the highest.” “Om is Brahman.”