Majma al-Zawaid 4416 — Buried treasure and mines

It is narrated from him that he said: I heard the Prophet (peace and blessings be upon him) say: "Minerals will appear in the land of Banu Sulaym, called Fir'awn or Fir'an (and in the speech of Abu Jahm these two words are almost the same). The worst of people will go out to it, (the narrator is in doubt, or perhaps the words are:) the worst of people will be gathered to it."
Abu Ya'la recorded it, and its narrators are thiqat (trustworthy).