Musnad Ahmad 30:3339

Yazid narrated to us, he said: And Muhammad informed us, from Abu Salamah, from Abu Hurairah, 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)."