Musnad Ahmad 11:6

Isma'il ibn 'Umar narrated to us, Isra'il narrated to us, from al-Hajjaj ibn Artah, from al-Walid ibn Abi Malik, from al-Qasim, from Abu Umamah, who said: A man from the Muslims granted protection to a man, while Abu Ubaydah ibn al-Jarrah was in command of the army. Khalid ibn al-Walid and 'Amr ibn al-'As said: "Do not grant him protection." Abu Ubaydah said: "We grant him protection. I heard the Messenger of Allah, peace and blessings of Allah be upon him, say: 'Any one of the Muslims may grant protection on behalf of the Muslims.'"