Library Eusebius of Caesarea Life of Constantine
Book 2, Chapter 73: The Controversy continues without Abatement, even after the Receipt of This Letter.
In this manner the pious emperor endeavored by means of the foregoing letter to promote the peace of the Church of God. And the excellent man to whom it was entrusted performed his part not merely by communicating the letter itself, but also by seconding the views of him who sent it; for he was, as I have said, in all respects a person of pious character. The evil, however, was greater than could be remedied by a single letter, insomuch that the acrimony of the contending parties continually increased, and the effects of the mischief extended to all the Eastern provinces. These things jealousy and some evil spirit who looked with an envious eye on the prosperity of the Church, wrought.
English translation by Ernest Cushing Richardson, in Nicene and Post-Nicene Fathers, Series II, Vol. I (eds. Philip Schaff and Henry Wace; Buffalo: Christian Literature Publishing Co., 1890). Public domain. Digital text via New Advent Church Fathers.