Chapter XXVII. On the temptation of Abbot Moses.
Works of St John Cassian (Institutes, Conferences, On the Incarnation) · Saint John Cassian
But the second person whom we mentioned as living in this desert, although he was also a remarkable and striking man, yet, in order to punish a single word, to which in a dispute with Abbot Macarius, he had given utterance somewhat too sharply, as he was anticipated in some opinion, he was instantly delivered to so dreadful a demon that he filled his mouth with filth which he supplied, and the Lord showed by the quickness of his cure, and the author of his healing, that He had brought this scourge upon him to purify him, that there might not remain in him any stain from his momentary error: for as soon as Abbot Macarius committed himself to prayer, quicker than a word the evil spirit fled away from him and departed.
Cassian 2.164.2