Masruq narrates that among the Companions of the Messenger of Allah (peace and blessings be upon him), those expert in the office of judgeship (qada) were six: Sayyiduna Umar, Sayyiduna Ali, Sayyiduna Abdullah, Sayyiduna Ubayy, Sayyiduna Zayd and Sayyiduna Abu Musa (may Allah be pleased with them). This is how it was narrated to us, but in most narrations, and the more authentic ones, Sayyiduna Mu'adh bin Jabal (may Allah be pleased with him) is mentioned in place of Sayyiduna Abu Musa.

Abu Mushir narrates that the Messenger of Allah (peace and blessings be upon him) gave Sayyiduna Ubayy bin Ka'b (may Allah be pleased with him) the title "Sayyid al-Ansar" (leader of the Ansar), and before his death people had begun calling him "Sayyid al-Muslimin" (leader of the Muslims).