Musnad Ahmad 1698
Hadeeth of Abu 'Ubaidah bin al-Jarrah, whose name was 'Amir bin Abdullah
It was narrated that ‘Amir said: The Messenger of Allah (ﷺ) sent the army of Dhatus-Salasil; he appointed Abu "Ubaidah in charge of the Muhajireen and "Amr bin al-’As in charge of the Bedouin, and he said to them both: "Cooperate with one another.” And they were instructed to raid [the tribe of] Bakr. So "Amr set out and raided [the tribe of ] Quda"ah, because Bakr were his maternal uncle. Al-Mugheerah bin Shu"bah went to Abu "Ubaidah and said: The Messenger of Allah (ﷺ) has appointed you over us, but the son of so and so [i.e., ‘Amr) is leading the people and you should have nothing to do with him [because he did the wrong thing] Abu "Ubaidah said: The Messenger of Allah (ﷺ) commanded us to cooperate with one another, and I shall obey the Messenger of Allah (ﷺ) even if "Amr disobeys him.