From Sahih Bukhari (Hadith 7119):
Narrated Abu Huraira:Allah's Messenger (ﷺ) 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 Abu Huraira that the Prophet (ﷺ) said the same but he said, "It (Euphrates) will uncover a mountain of gold (under it)
Reference: Bukhari 7119