Musnad Abu Ya'la al-Mawsili 8:7

Muhammad ibn Isma'il narrated to us, Sulayman ibn Hayyan narrated to us, from Hajjaj, from al-Walid ibn Abi Malik, from 'Abd al-Rahman ibn Maslamah: That a man from the Muslims granted protection to a man from the polytheists. Khalid ibn al-Walid and 'Amr said, "Do not grant protection." Abu 'Ubaydah said, "You grant him protection. I heard the Messenger of Allah (peace and blessings of Allah be upon him) saying: 'Some of the Muslims grant protection on behalf of all of them.'"