The Gospel of Barnabas, which purports to depict the life of Jesus is currently widely published in Islamic circles. Though it was never mentioned by Islamic writers, and though claims that it was mentioned by Irenaeus cannot be tied any text, and though no early manuscripts exist or even any early references to such a gospel, it existed in at least two manuscripts, the Italian and the Spanish.
The Italian manuscript survives in a library in Austria, while the Spanish manuscript was lost in the eighteenth or nineteenth centuries; however an eighteenth century copy of the original Spanish manuscript was discovered in the 1970s in the University of Sydney's Fisher library. The Italian manuscript contains chapter rubrics and margin notes in Arabic; the margin notes form a rough Arabic translation of selected passages.
The Gospel of Barnabas was little known outside academic circles until recent times, when a number of Muslims have taken to publishing it in order to attempt to refute Christianity. It resonates better with existing Muslim views than with Christianity because it foretells the coming of Muhammad by name, and reports that Jesus was not the Messiah but rather a "prophet of salvation" whose mission was restricted to the "house of Israel". Rather than describing the crucifixion of Jesus, it describes him being raised up into heaven, similar to the description of Elijah in 2 Kings, Chapter 2. Furthermore, some Muslims claim that Barnabas himself wrote the Gospel, and that the Gospels of Matthew, Mark, Luke and John were written by followers of Paul long after the events they describe, and that therefore the Gospel of Barnabas is more authentic than the other Gospels. There is some difficulty reconciling the Gospel of Barnabas (which asserts that Muhammad is the Messiah) with the Qur'an (which gives this title to Jesus).
The Gospel of Barnabas makes naive errors in geography, has Barnabas sailing to land-locked Nazareth, had Jesus born and current politics of Palestine, does not realize that 'Christ' means 'anointed.'
It should not be confused with the Epistle of Barnabas, which may have been written in 2nd Century Alexandria. There is no link between the two books in style, content or history. On the issue of circumcision, the two authors clearly hold very different views, that of the 'Epistle' in rejecting Jewish practices and that of the 'Gospel' in promoting Muslim ones.