Two versions of the formerly lost Holy Book of the Great Invisible Spirit, also inappropriately called the Coptic Gospel of the Egyptians (which is quite distinct from the Greek Gospel of the Egyptians), were among the codices in the Nag Hammadi library, discovered in 1945.
The main contents concern the SethianGnostic understanding of how the earth came into being, how Seth, in the Gnostic interpretation, is incarnated as Jesus in order to release people's souls from the evil prison that is creation.
It also contains a hymn, parts of which are unusual in being apparently meaningless sequences of vowels (thought to be a representation of early Christian glossolalia), although the vowels of the final paragraph (u aei eis aei ei o ei ei os ei) can be partitioned to read (in Greek) who exists as Son for ever and ever. You are what you are, you are who you are.
^John D. Turner: "Since the late 1940s it has become customary to refer to it inappropriately as the Gospel of the Egyptians." Meyer, Marvin (2007). The Nag Hammadi Scriptures: International Edition. p. 247.