(10) باب مَنْ قَاتَلَ لِلْمَغْنَمِ هَلْ يَنْقُصُ مِنْ أَجْرِه
Narrated Abu Musa Al-Ash`ari:
A bedouin asked the Prophet, "A man may fight for the sake of booty, and another may fight so that he may be mentioned by the people, and a third may fight to show his position (i.e. bravery); which of these regarded as fighting in Allah's Cause?" The Prophet (ﷺ) said, "He who fights so that Allah's Word (i.e. Islam) should be superior, fights for Allah's Cause."
Reference: Sahih al-Bukhari 3126
In-book reference: Book 57, Hadith 35
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 4, Book 53, Hadith 355