This passage comes from the Benedicta Ward translation of The Sayings of the Desert Fathers:
A brother went out to the cell of Arsenius in Scetis, and looked in through the window, and saw him like fire from head to foot. (He was a brother worthy to see such sights.) When he knocked, Arsenius came out, and saw the brother standing there amazed, and said to him, 'Have you been knocking long? Did you see anything?' He answered, 'No.' After talking with him, Arsenius sent him on his way.
As an aside to our resident doubting-Thomas Asteriktos
, I just wanted to point to this as another example of 'moral lying' within Christianity, one of his noted contradictions in the Christian faith.