Tasks Entrusted by the First Two Khulafa

When Hazrat Abu Bakr (ra) was bestowed the mantle of Khilafat, he appointed Hazrat Abu Ubaidah (ra) to oversee the affairs of the Bait-ul-Mal. In 13 AH, when Hazrat Abu Bakr (ra) sent an army to Syria, he appointed Hazrat Abu Ubaidah (ra) as its commander. Later, when Hazrat Umar (ra) was bestowed the mantle of Khilafat, he removed Hazrat Khalid (ra) bin Waleed as the commander-in-chief and replaced him with Hazrat Abu Ubaidah (ra).

(Siyar A‘lam al-Nubala li Imam al-Dhahabi, Vol. 1, p. 15, Abu Ubaidah bin al-Jarrah, Dar al-Risalah al-Alamiyyah, Damascus, 2014)