Gregory Nazianzus

To speak concisely, the Godhead is undivided in separate persons. There is one mingling of light, as though three suns are joined to each other. When then we consider the Godhead, or the first cause, or the undivided majestic unity, that which we conceive is one. However, when we consider the persons in whom the Godhead dwells, those who timelessly and with equal glory have their being from the first cause, there are three whom we worship."