Sahih Bukhari Volume 002, Book 017, Hadith Number 149.

Narated By Ibn 'Umar : Allah's Apostle (p.b.u.h) said, "Keys of the unseen knowledge are five which nobody knows but Allah... nobody knows what will happen tomorrow; nobody knows what is in the womb; nobody knows what he will gain tomorrow; nobody knows at what place he will die; and nobody knows when it will rain."

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