Sahih Bukhari Volume 9, Book 88, Hadith Number 235.

Narrated By Abu Huraira : Allah’s Apostle said, “Soon the river “Euphrates” will disclose the treasure (the mountain) of gold, so whoever will be present at that time should not take anything of it.” Al-A’raj narrated from Abii Huraira that the Prophet said the same but he said, “It (Euphrates) will uncover a mountain of gold (under it).”