It is narrated from Ibn Umar (radiyAllahu 'anhu), that The Prophet (sallAllahu 'alaihi wa salam) 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."

 
[Bukhari: Book 9 Vol 93 Hadith 476]