Hazrat Umar (ra) introduced many beneficial initiatives during his Khilafat, one of which was the formation of a consultative body [Majlis-e-Shura]. The system of Majlis-e-Shura was established during the era of Hazrat Umar (ra). This consultative body was formed of prominent companions from among the Muhajireen and Ansar and Hazrat Ubayy (ra) bin Kaab was also its member in representation of the Khazraj tribe.
(Sheikh Shah Moinuddin Ahmad Nadvi, Siyar al-Sahabah, Vol. 3 [Karachi, Pakistan: Dar al-Isha‘ah Urdu Bazar, 2004] 142-143)