كتاب الإمارة
33
The Book on Government
(45)
Chapter: The words of the prophets saws: "Deeds are but with intentions" which includes fighting and other deeds
(45)
باب قَوْلِهِ صلى الله عليه وسلم ‏"‏ إِنَّمَا الأَعْمَالُ بِالنِّيَّةِ.‏"‏ وَأَنَّهُ يَدْخُلُ فِيهِ الْغَزْوُ وَغَيْرُهُ مِنَ الأَعْمَالِ

It has been narrated on the authority of Umar b. al-Khattab that the Messenger of Allah (ﷺ) said:

(The value of) an action depends on the intention behind it. A man will be rewarded only for what he intended. The emigration of one who emigrates for the sake of Allah and His Messenger (ﷺ) is for the sake of Allah and His Messenger (ﷺ) ; and the emigration of one who emigrates for gaining a worldly advantage or for marrying a woman is for what he has emigrated.
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ بْنِ قَعْنَبٍ، حَدَّثَنَا مَالِكٌ، عَنْ يَحْيَى بْنِ سَعِيدٍ، عَنْ مُحَمَّدِ، بْنِ إِبْرَاهِيمَ عَنْ عَلْقَمَةَ بْنِ وَقَّاصٍ، عَنْ عُمَرَ بْنِ الْخَطَّابِ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏ "‏ إِنَّمَا الأَعْمَالُ بِالنِّيَّةِ وَإِنَّمَا لاِمْرِئٍ 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 ‏"‏ ‏.‏
Reference : Sahih Muslim 1907 a
In-book reference : Book 33, Hadith 222
USC-MSA web (English) reference : Book 20, Hadith 4692
  (deprecated numbering scheme)