Sahih Bukhari | Volume 8 | Hadith Number 518

Narrated by 'Aisha
Some rough bedouins used to visit the Prophet and ask him, "When will the Hour be?" He would look at the youngest of all of them and say, "If this should live till he is very old, your Hour (the death of the people addressed) will take place." Hisham said that he meant

(by the Hour), their death.