The only proof of His existence is union with Him. The world disappears in Him. He is the peaceful, the good, the ONE without a second. This is the fourth condition of the Self- The most worthy of all. This is the Atman.
Brahman is AUM
Atman, smaller than the small, greater than the great, is hidden in the hearts of all living creatures. A man who is free from desires beholds the majesty of the Self through tranquility of the senses and the mind and becomes free from grief.