Volume 1, Book 2, Number 51:Saheeh Bukhari
Narrated 'Umar bin Al-Khattab:
Allah's Apostle said, "The reward of deeds depends upon the intention and every person will get the reward according to what he has intended. So whoever emigrated for Allah and His Apostle, then his emigration was for Allah and His Apostle. And whoever emigrated for worldly benefits or for a woman to marry, his emigration was for what he emigrated for."