Nafi' bin Abd al-Harith al-Khuza'i (may Allah be pleased with him) met Umar bin al-Khattab (may Allah be pleased with him) at a place called Usfan. Umar (may Allah be pleased with him) had appointed him governor over the people of Makkah. He greeted Umar (may Allah be pleased with him) with salam, and Umar (may Allah be pleased with him) asked: "Whom have you appointed as your deputy over this valley?" He said: "I have come after appointing Ibn Abza as deputy." Umar (may Allah be pleased with him) asked: "Who is Ibn Abza?" He said: "He is one of our freed slaves." Umar (may Allah be pleased with him) said: "You appointed a freed slave as deputy!" He said: "O Commander of the Believers! He is a reciter of the Qur'an and knowledgeable in the shares of inheritance (fara'id)." Umar (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said: "Indeed, Allah Almighty raises many people through this Book and brings many others low through it."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5125