Sahih Bukhari Volume 7, Book 62, Hadith Number 8.

Narrated By ‘Umar bin Al-Khattab : The Prophet said, “The rewards (of deeds) are according to the intention, and everybody will get the reward for what he has intended. So whoever emigrated for Allah’s and His Apostle’s sake, his emigration was for Allah and His Apostle; and whoever emigrated for worldly benefits, or to marry a woman, then his emigration was for the thing for what he emigrated for.”