Musnad Ahmad 30:1958

Yahya ibn Ishaq narrated to us, Ibn Lahi'ah narrated to us, from al-Harith ibn Yazid, from Abu 'Alqamah, 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 of the religion."