Imaam Ahmad b. Muhammad b. Hanbal ash-Shaibaanee (died 241AH, rahimahullaah) reports in his Musnad (no. 232):
Abu Kaamil narrated to us saying: Ibraaheem b. Sa`ad narrated to us saying: Ibn Shihaab narrated to us: and `Abdur-Razzaaq narrated to us saying: Ma`mar informed us from az-Zuhree, from Abu Tufail `Aamir b. Waathilah that:
[Also Saheeh Muslim, no. 817.]
Naafi` b. `Abdul-Haarith met `Umar b. al-Khattaab (radiyallaahu `anhu) in `Usfaan – and `Umar had appointed him in charge over Makkah. So `Umar said to Naafi`: “Who have you appointed as your deputy over the people of the valley (i.e. Makkah)?”
Naafi` replied: “I have appointed over them Ibn ‘Abzaa.”
`Umar asked: “And who is Ibn ‘Abzaa?”
Naafi` replied: “One of our freed slaves.”
`Umar said: “You have appointed a freed slave over them?!”
Naafi` responded: “He is proficient in the Book of Allaah having much knowledge of it, he is a scholar in the rules of inheritance and a judge.”
Upon that `Umar said: “Indeed your Prophet (salallaahu `alaihi wassallam) said: Surely Allaah raises people by way of this Book and makes others lowly by way of it.”
So it is the Religion of Islaam, the Book of Allaah, the Sunnah of the Prophet (salallaahu `alaihi wassallam) that is the measure of a person’s worth – not the colour of one’s skin, or the wealth one possesses or his lineage. Allaah raises people who are sincere and truthful in their adherence to His Religion and remain steadfast upon that until they meet their Lord. They read and study the Book of Allaah, they are acquainted with the Prophetic traditions and their meanings, because they learn that from the Scholars of Sunnah.
And He (the Most High) makes lowly those who are insincere and untruthful – those who give no concern to the Sunnah and raise the banner of opposition to the Book and Sunnah, and forsake the Truth and its people.