Library Eusebius of Caesarea Life of Constantine
Book 1
Chapter 4: That God honored Constantine
And God himself, whom Constantine worshipped, has confirmed this truth by the clearest manifestations of his will, being present to aid him at the commencement, during the course, and at the end of his reign, and holding him up to the human race as an instructive example of godliness. Accordingly, by the manifold blessings he has conferred on him, he has distinguished him alone of all the sovereigns of whom we have ever heard as at once a mighty luminary and most clear-voiced herald of genuine piety.
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.