The Secret Book of John (Apocryphon of John) is a 2nd-century AD Sethian Gnostic

Gnosticism

Gnosticism is a scholarly term for a set of religious beliefs and spiritual practices common to early Christianity, Hellenistic Judaism, Greco-Roman mystery religions, Zoroastrianism , and Neoplatonism.A common characteristic of some of these groups was the teaching that the realisation of Gnosis...

 text of secret teachings. Since it was known to the church father Irenaeus, it must have been written before around AD 180. It describes Jesus Christ appearing and giving secret knowledge (gnosis

Gnosis

Gnosis is the common Greek noun for knowledge . In the context of the English language gnosis generally refers to the word's meaning within the spheres of Christian mysticism, Mystery religions and Gnosticism where it signifies 'spiritual knowledge' in the sense of mystical enlightenment.-Related...

) to the apostle John

John the Apostle

John the Apostle, John the Apostle, John the Apostle, (Aramaic Yoħanna, (c. 6 - c. 100) was one of the Twelve Apostles of Jesus. He was the son of Zebedee and Salome, and brother of James, another of the Twelve Apostles...

. The author describes this having occurred after Jesus "has gone back to the place from which he came".