Allah Upanishad, or Allopanishad, is a book of dubious origin supposedly from Atharvaveda and believed to be written during Mughal Emperor Akbar's reign.
Swami Dayananda Saraswati's book Satyarth Prakash (The Light of Truth) argues that the Allopanishad is not part of the Upanishad canon. It does not even appear in the Atharvaveda. The book could have been written during the Mughal era (possibly during Akbar's reign).[1][2]