Musannaf Ibn Abi Shayba 33:257

Yahya ibn Adam narrated to us, he said: Hammad ibn Salamah narrated to us, from Abu Na'amah, from Hujayr ibn Rabi', who said: Umar said: "Indeed, wickedness is like this," and he covered his head down to his eyebrows. "Verily, righteousness is like this," and he uncovered his head.