Musannaf Ibn Abi Shayba 28:859

'Abd al-Rahim ibn Sulayman narrated to us, from al-Hajjaj, from al-Walid ibn Abi Malik, from 'Abd al-Rahman ibn Salama, that a man granted protection (aman) to a group of people while he was with 'Amr ibn al-'As, Khalid ibn al-Walid, and Abu 'Ubaydah ibn al-Jarrah. 'Amr and Khalid said, "We do not grant protection to those whom he has granted protection." Abu 'Ubaydah said, "I heard the Messenger of Allah, may Allah bless him and grant him peace, say: 'Some of the Muslims grant protection on behalf of all the Muslims.'"