“When [Gregory] was passing a sleepless night because of these worries, someone appeared to him in human form, aged in appearance, clothed in garments denoting a sacred dignity, with a face characterized by a sense of grace and virtues. Gregory, looking frightened, rose from his bed and asked him who he was and why he had come. The other, in a subdued voice, after soothing his distress, told Gregory that he had appeared by divine will, because of the questions that Gregory found ambiguous and confusing, to reveal to him the truth of pious faith. After hearing these words, Gregory regained his serenity and began to observe the other man with a certain joy and wonder.
The other then held up his hand, as if to point out, with his index finger, something that had appeared opposite to him. Gregory, turning his gaze in the direction indicated by the other man’s hand, saw before him another figure, which had appeared not long before. This figure had the appearance of a woman, whose noble aspect far surpassed normal human beauty. Gregory was again disturbed. Turning away his face, he averted his glance and was filled with perplexity; nor did he know what to think of this apparition, which he could not bear to look upon with his eyes. For the extraordinary character of the vision lay in this: that though it was a dark night, a light was shining, and so was the figure that had appeared to him, as if a burning lamp had been kindled there.
Although he could not bear to look upon the apparition, Gregory heard the speech of those who had appeared, as they discussed the problems that were troubling him. From their words, Gregory not only obtained an exact understanding of the doctrine of the faith but also was able to discover the names of the two persons who had appeared to him, for they called each other by name.
For it is said that he heard the one who had appeared in womanly form exhorting John the Evangelist to explain to the young man the mystery of the true [faith]. John, in his turn, declared that he was completely willing to please the Mother of the Lord even in this matter and that this was the one thing closest to his heart. And so the discussion coming to a close, and after they had made it quite clear and precise for him, the two disappeared from his sight.”Gregory of Nyssa, Life of St. Gregory the Wonderworker, PG 14, 909-12
Gambero, L., 1999. Mary and the Fathers of the Church 1st ed. Translated by Buffer, T., San Francisco: Ignatius Press. p.93-94