The Great Hymn to the Aten, by Pharaoh Akhenaten. This hymn was written by Akhenaten for Aten with whom Atenism was devoted. In it he forbade the worship of other gods and this was a huge departure for the time.
This scholarly article gives insight into the similarities shared between Atenism and early Judaism. One of the striking similarities between the two religions was the Great Hymn and Psalms 104 indicating that perhaps Judaism used elements from Atenism in its early development.
This Hymn was written to Aten in praise of his greatness. While there are not a lot of first hand accounts of the religion during ancient Egypt what we are left with is are the original Hymns in praise of Aten.
This is a link to some of the art that was done during the reign of the Pharaoh Akhenaten. This art is important because this is what tells us about the life and time during his reign and also gives a glimpse into what the religion was all about.