مُسْنَدُ أَحْمَدَ
Musnad Ahmad 1695
Hadeeth of Abu 'Ubaidah bin al-Jarrah, whose name was 'Amir bin Abdullah
It was narrated from al-Qasim that Abu Umamah said: A man among the Muslims granted protection to a man when Abu ‘Ubaidah bin al-Jarrah was in charge of the army, Khalid bin al-Waleed and "Amr bin al-"As said: You should not acknowledge his protection. But Abu "Ubaidah said. We will grant him protection, I heard the Messenger of Allah (ﷺ) say: “One of the Muslims may grant protection and it is binding upon all the Muslims."
Musnad Ahmad 1695Hasan because of corroborating evidence; this is a Da'if isn