Athanasius of Alexandria

The bishops [at the Council of Nicea], having detected the Arians' deceitfulness in this matter, collected from Scripture those passages that say of Christ that he is the glory, the fountain, the stream and the express image of the person; and they quoted the following words: "In your light we shall see light"; and likewise, "I and the Father are one." They, then, with still greater clearness, briefly declared that the Son is of one substance [homoousios] with the Father; for this, indeed, is the signification of the passages that have been quoted.