From what I have heard so far, it is said that the Narayana Upanishad (not to be confused with the Mahanarayana Upanishad of Taittiriya Aranyaka) has been quoted by Shripaada Adi Shankaracharya and Shripaada Ramanujacharya. However, till now, I have not found anyone providing an exact reference of them quoting it. Some say that it has been quoted in Shripaada Adi Shankaracharya's Vishnu-Sahasranama Bhashya, but its authenticity is uncertain and it is also believed to be a similar passage from the Atmabodha Upanishad and not the Narayana Upanishad.
So, my question is: Is the Narayana Upanishad authentic and is there a reference of a reputed saint quoting it before the 15th century, preferably Shripaada Adi Shankaracharya, Shripaada Ramanujacharya or Shripaada Madhvacharya, in works such as Upanishad or Brahma Sutra Bhashyas?