Musnad Abu Ya'la al-Mawsili 118:39

Salih ibn Malik Abu Abd Allah narrated to us, Abd al-Razzaq ibn Umar al-Thaqafi narrated to us, from al-Zuhri, from Anas ibn Malik, who said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "Indeed, for every nation there is a trustee, and this is our trustee." And he took the hand of Abu Ubaydah ibn al-Jarrah.