Complex sentence: The account of Paphnutius the Ascetic, who encountered him in the Egyptian desert, forms the sole source for our knowledge of the life of Saint Onuphrius, who became a monk at a cenobitic monastery near Thebes, which he left to lead an eremitic life.
Split into simpler sentences: The account of Paphnutius the Ascetic, who encountered him in the Egyptian desert, forms the sole source for our knowledge of the life of Saint Onuphrius. Onuphrius became a monk at a cenobitic monastery near Thebes, which he left to lead an eremitic life.