Sunan Ibn Majah, Chapter: The Book of the Sunnah

It was narrated that Nafi bin Abdul-Harith met Umar bin Khattab in Usfan, when Umar had appointed him as his governor in Makkah. Umar asked: "Whom have you appointed as your deputy over the people of the valley?" He said: "I have appointed Ibn Abza over them." Umar said: "Who is Ibn Abza?" Nafi said: "One of our freed slaves." Umar said: "Have you appointed a freed slave over them?" Nafi said: "he has great knowledge of the Book of Allah, is well versed in the rules of inheritance (Fara'id) and is a (good) judge." Umar said: "Did not your Prophet (saw) say: 'Allah raises some people (in status) because of this Book and brings others low because of it?'" (Sahih)