Musnad Abu Ya'la al-Mawsili 2:89

Abu Hisham narrated to us, Abu Usamah narrated to us, Umar bin Hamzah narrated to us, from Salim, from Ibn Umar, from Umar, from the Prophet (may Allah bless him and grant him peace), who said: "Indeed, for every nation there is a trustworthy one, and the trustworthy one of this nation is Abu Ubaydah bin al-Jarrah."