Musnad Ahmad 30:425

Abdullah ibn Numayr narrated to us, Muhammad—meaning Ibn Amr—narrated to us, from Abu Salamah, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "People are like mines; the best of them in the Pre-Islamic Period (Jahiliyyah) are the best of them in Islam, if they attain understanding (fiqh)."