They used to say of Abba Sarmatas that, on the advice of Abba Poemen, he often undertook to fast for forty days and the days went by like nothing in his sight. So Abba Poemen came to him and said to him: “Tell me, what have you seen while enduring such toil?” “Not much,” he said to him. Abba Poemen said to him: “I will not let you go unless you tell me.”  “I found out only one thing,” he said: “that if I say to sleep: ‘Go away,’ away it goes; and if I say: ‘Come,’ come it does.”

Give Me a Word: The Alphabetical Sayings of the Desert Fathers