Musannaf Ibn Abi Shayba 27:657

Isma'il ibn 'Ulayyah narrated to us, from Khalid, from Abu Qilabah, who said: Anas said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Indeed, for every nation there is a trustee, and our trustee, O this nation, is Abu 'Ubaydah ibn al-Jarrah."