When Abba Macarius was returning from the marsh to his cell one day carrying some palm-leaves, he met the devil on the road with a scythe. The latter struck at him as much as he pleased, but in vain, and he said to him, “What is your power, Macarius, that makes me powerless against you? All that you do, I do, too; you fast, so do I; you keep vigil, and I do not sleep at all; in one thing only do you beat me.” Abba Macarius asked what that was. He said, “Your humility. Because of that I can do nothing against you.”
The Sayings of the Desert Fathers. The Alphabetical Collection, translated by Benedicta Ward, SLG, (Kalamazoo: Cistercian Publications, 1975 ) 129-130.