Musannaf Ibn Abi Shayba 23:63

Narrated to us al-Muqri’, from Sa’id ibn Abi Ayyub, from Ibn ‘Ajlan, from al-Qa’qa’, from Abu Salih, from Abu Hurayrah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "The most complete of the believers in faith are those of them with the best character."