It is narrated from Sayyiduna Abdullah bin Amr (may Allah be pleased with them both) that he said: "Various kinds of mines will appear. One of them will be near the Hijaz, to which the worst of people will come; it will be called 'Fir'awn'. While they are working in it, gold will suddenly appear from it, and they will be delighted with working there, when suddenly it and all of them will be swallowed up by the earth." This hadith has an authentic (sahih) chain of narration, but the two Shaykhs (Bukhari and Muslim) did not record it.