From Peter of Damascus, A Treasury of Divine Knowledge:
In our ignorance, however, we should not identify God in Himself with His divine attributes, such as His goodness, bountifulness, justice, holiness, light, fire, being, nature, power, wisdom, and the others…God in Himself is not among any of the things that the intellect is capable of defining, for He is undetermined and undeterminable. In theology we can speak about the attributes of God but not about God in Himself…It is indeed more correct so speak of God in Himself as inscrutable, unsearchable, inexplicable, as all that is impossible to define. For He is beyond intellection and thought, and is known only to Himself, one God in three hypostases, unoriginate, unending, beyond goodness, above all praise. All that is said of God in divine Scripture is said with this sense of our inadequacy, that though we may know that God is, we cannot know what He is; for in Himself He is incomprehensible to every being endowed with intellect and reason.