Library Eusebius of Caesarea Life of Constantine
Book 2, Chapter 57: He gives Glory to God, who has given Light by his Son to those who were in Error.
And truly our worship is no new or recent thing, but one which you have ordained for your own due honor, from the time when, as we believe, this system of the universe was first established. And, although mankind have deeply fallen, and have been seduced by manifold errors, yet have you revealed a pure light in the person of your Son, that the power of evil should not utterly prevail, and hast thus given testimony to all men concerning yourself.
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.