Musannaf Ibn Abi Shayba 21:704

Ahmad ibn Ishaq narrated to us, from Abd al-Wahid ibn Ziyad, who said: A sheikh from Quraysh narrated to me, from Ibn Hakim, who said: Umar ibn al-Khattab said to me: The Messenger of Allah (peace and blessings of Allah be upon him) said to him: "O son of al-Khattab, say: O Allah, make my inner self better than my outer self, and make my outer self righteous."