The Upanishads are considered sacred scriptures by the Hindus.

The following verses from the Upanishads refer to the Concept of God:

1. "Ekam evadvitiyam"
   "He is One only without a second." [Chandogya Upanishad 6:2:1]

    

2. "Na casya kascij janita na cadhipah."
   "Of Him there are neither parents nor lord." [Svetasvatara Upanishad 6:9]

3. "Na tasya pratima asti"
   "There is no likeness of Him." [Svetasvatara Upanishad 4:19]

4. The following verses from the Upanishad allude to the inability of man to imagine God in a particular form:

   "Na samdrse tisthati rupam asya, na caksusa pasyati kas canainam."
   "His form is not to be seen; no one sees Him with the eye."  [Svetasvatara Upanishad 4:20]