Tradition
St. Jerome
De Viris Illustribus (Illustrious Men)
Chapter 31
Musanus, not inconsiderable among those who have written on ecclesiastical doctrine, in the reign of Marcus Antoninus Verus wrote a book to certain brethren who had turned aside from the church to the heresy of the Encratites.
Source: De Viris Illustribus (Illustrious Men) (New Advent)