Musnad Ahmad 30:3166

Hassan ibn Musa narrated to us, Hammad ibn Salamah narrated to us, from Ammar ibn Abi Ammar, from Abu Hurairah, who said: The Messenger of Allah, peace and blessings of Allah be upon him, said: "People are like mines in goodness and evil. The best of you in the Pre-Islamic Period (Jahiliyyah) are the best of you in Islam, if they attain understanding (fiqh)."