Sahih Bukhari Volume 9, Book 93, Hadith Number 476.

Narrated By Ibn Umar : The Prophet said, “The keys of the unseen are five and none knows them but Allah:
  1. None knows what is in the womb, but Allah:
  2. None knows what will happen tomorrow, but Allah;
  3. None knows when it will rain, but Allah;
  4. None knows where he will die, but Allah (knows that);
  5. And none knows when the Hour will be established, but Allah.”