Musnad Ahmad 30:3686

Abdullah ibn Yazid narrated to us, Sa'id narrated to us, Ibn 'Ajlan narrated to me, from al-Qa'qa' ibn Hakim, from Abu Salih, from Abu Hurayrah, who said: The Messenger of Allah, peace and blessings of Allah be upon him, said: "The most complete of the believers in faith are those of them with the best character."