Musannaf Ibn Abi Shayba 13:1961

Abu Bakr narrated to us, he said: Abu Khalid al-Ahmar narrated to us, from Layth, from Mujahid, who said: Umar said: "There are three whose rights are not belittled except by a hypocrite: a just leader, a teacher of good, and one with gray hair in Islam."