Musannaf Ibn Abi Shayba 17:1374

Abu Usama narrated to us, from Za'ida, from Mansur, from Mujahid, who said: It reached Umar that a governor of his did not take a midday nap (qaylula). So Umar wrote to him: "Take a midday nap, for I have been told that the devil does not take a midday nap." Mujahid said: "Indeed, the devils do not take a midday nap."