VI.ii.12. When Julian the Apostate was invading Persia he sent a demon back westwards to report on what was happening there. But when it arrived at a certain spot where there was a hermit it stopped short for ten days and was unable to go any further because of the ceaseless prayer which the hermit was offering. It returned to its sender having achieved nothing. Julian asked it why it had stopped and it replied that it had had to stop and turn
back having done nothing because it had waited ten days for the monk Publius to
stop praying and let him pass. “He didn’t stop,” he continued, “and so I couldn’t pass and I
turned back with nothing done.”
In a dreadful rage Julian cried that he would exact vengeance on him when he returned. But in the providence of God he was slain a few days after, whereupon one of the army commanders with him turned back immediately, sold all that he had, gave it to the poor, and joined that old man to become a monk, and so found his peace in God.
De Vitis Patrum VI, Libelus 2