Library Eusebius of Caesarea Life of Constantine
Book 2, Chapter 18: Death of Licinius, and Celebration of the Event.
He then proceeded to deal with this adversary of God and his followers according to the laws of war, and consign them to fitting punishment. Accordingly the tyrant himself, and they whose counsels had supported him in his impiety, were together subjected to the just punishment of death. After this, those who had so lately been deceived by their vain confidence in false deities, acknowledged with unfeigned sincerity the God of Constantine, and openly professed their belief in him as the true and only God.
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.