Library Eusebius of Caesarea Life of Constantine
Book 1, Chapter 24: It was by the Will of God that Constantine became possessed of the Empire.
Thus then the God of all, the Supreme Governor of the whole universe, by his own will appointed Constantine, the descendant of so renowned a parent, to be prince and sovereign: so that, while others have been raised to this distinction by the election of their fellow-men, he is the only one to whose elevation no mortal may boast of having contributed.
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.