Musnad Ahmad 30:3167

'Affan narrated to us, Hammad narrated to us, he said: 'Ammar ibn Abi 'Ammar informed us, he said: I heard Abu Hurairah, he said: I heard Abu al-Qasim (may Allah bless him and grant him peace) say: "People are like mines in goodness and evil. The best of them in the Pre-Islamic Period (Jahiliyyah) are the best of them in Islam, if they attain understanding (fiqh)."