Tradition
St. Jerome
De Viris Illustribus (Illustrious Men)
Chapter 128
Gregory bishop of Nyssa, the brother of Basil of Cæsarea, a few years since read to Gregory Nazianzan and myself a work against Eunomius. He is said to have also written many other works, and to be still writing.
Source: De Viris Illustribus (Illustrious Men) (New Advent)