The Book on Government
33/42. Chapter:
One who fights so that the word of Allah will be supreme is fighting in the cause of Allah
Sahih Muslim
وَحَدَّثَنَاهُ إِسْحَاقُ بْنُ إِبْرَاهِيمَ، أَخْبَرَنَا عِيسَى بْنُ يُونُسَ، حَدَّثَنَا الأَعْمَشُ، عَنْ شَقِيقٍ، عَنْ أَبِي مُوسَى، قَالَ أَتَيْنَا رَسُولَ اللَّهِ صلى الله عليه وسلم فَقُلْنَا يَا رَسُولَ اللَّهِ الرَّجُلُ يُقَاتِلُ مِنَّا شَجَاعَةً . فَذَكَرَ مِثْلَهُ .
It has been narrated (through yet another chain of transmitters) on the same authority, i. e. Abu Musa, who said: We, came to the Messenger of Allah (ﷺ) and said: Messenger of Allah, one of us hho fights to display his valour... (followed by the same words as we have in the previous tradition).
Reference : Sahih Muslim 1904cIn-book reference : Book 33, Hadith 216USC-MSA web (English) reference : Book 20, Hadith 4686