Sahih Muslim Book 41, Hadith Number 6909.
Chapter : The events foretold by the Holy Prophet (may peace be upon him) about the last hour.
Hudhaifa reported that Allah’s Messenger (may peace be upon him) stood before us one day and he did not leave anything unsaid (that he had to say) at that very spot which would happen (in the shape of turmoil) up to the Last Hour. Those who had to remember them preserved them in their minds and those who could not remember them forgot them. My friends knew them and there are certain things which slip out of my mind, but I recapitulate them when anyone makes a mention of them just as a person is lost from one’s mind but is recalled to him on seeing his face.