Sahih al-Bukhari 54
Narrated 'Umar bin Al-Khattab:
Allah's Messenger (ﷺ) 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."
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ، قَالَ أَخْبَرَنَا مَالِكٌ، عَنْ يَحْيَى بْنِ سَعِيدٍ، عَنْ مُحَمَّدِ بْنِ إِبْرَاهِيمَ، عَنْ عَلْقَمَةَ بْنِ وَقَّاصٍ، عَنْ عُمَرَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏
"‏ الأَعْمَالُ بِالنِّيَّةِ، وَلِكُلِّ امْرِئٍ مَا نَوَى، فَمَنْ كَانَتْ هِجْرَتُهُ إِلَى اللَّهِ وَرَسُولِهِ، فَهِجْرَتُهُ إِلَى اللَّهِ وَرَسُولِهِ، وَمَنْ كَانَتْ هِجْرَتُهُ لِدُنْيَا يُصِيبُهَا، أَوِ امْرَأَةٍ يَتَزَوَّجُهَا، فَهِجْرَتُهُ إِلَى مَا هَاجَرَ إِلَيْهِ ‏"‏‏.‏