Sahih Al-Bukhari: Deeds (their correctness and rewards) depend upon intentions

Narrated `Umar bin Al−Khattab (MAPH): I heard Allah's Apostle (PBUH) saying, 

Deeds (their correctness and rewards) depend upon intentions, and every person gets but what he has intended. So whoever emigrated for worldly benefits, or for a woman to marry, his emigration is for what he emigrated for.

Al-Bukhari, As-Sahih, Kitab-al-Bad'al-Wahi, Number: 01