Musnad Abu Ya'la al-Mawsili 155:230

Muhammad ibn al-Muthanna narrated to us, Abd al-Wahhab narrated to us, Ayyub narrated to us, from Muhammad, from Abu Hurayrah, who said: I do not know it except from the Prophet, may Allah bless him and grant him peace, who said: "People are like mines in goodness and evil. The best of them in the Age of Ignorance are the best of them in Islam, if they attain understanding (fiqh)."