The oration by St. Gregory is provided in honor of St. Cyprian, commemorated on October 2.
Gregory of Nazianzus. Oration 24: On Cyprian. trans. Martha Vinson. In St. Gregory of Nazianzus: Select Orations, The Fathers of the Church: A New Translation, vol. 107. Washington, DC: Catholic University of America Press, 2003. pp. 39-71