Sahih Bukhari Volume 001, Book 003, Hadith Number 056.
Narated By Abu Huraira : While the Prophet was saying something in a gathering, a Bedouin came and asked him, "When would the Hour (Doomsday) take place?" Allah's Apostle continued his talk, so some people said that Allah's Apostle had heard the question, but did not like what that Bedouin had asked. Some of them said that Alllah's Apostle had not heard it. When the Prophet finished his speech, he said, "Where is the questioner, who enquired about the Hour (Doomsday)?" The Bedouin said, "I am here, O Allah's Apostle ." Then the Prophet said, "When honesty is lost, then wait for the Hour (Doomsday)." The Bedouin said, "How will that be lost?" The Prophet said, "When the power or authority comes in the hands of unfit persons, then wait for the Hour (Doomsday.)"