Missionary to Kufa
After the demise of the Holy Prophet (sa), Hazrat Umar (ra) appointed Hazrat Abdullah bin Mas‘ud as a missionary for the education and moral training of the people of Kufa and at the same time appointed Hazrat Ammar bin Yassir as the governor. Hazrat Umar (ra) then said to the people of Kufa, “Both of these individuals are among the close companions of the Holy Prophet (sa) and have a special standing. They were among the people who took part in the Battle of Badr. You all should follow their example and obey their directives and also listen to what they say. For you, I have given precedence to Abdullah bin Mas‘ud over me.”
(Usdul Ghaba, Vol. 3, p. 385, Dar-ul-Kutub Al-ilmiyyah, Beirut)