ENOfficial
It was narrated that Abu Ja'far said: "I was sitting with Suwaid bin Muqarrin, and he said: The Messenger of Allah (ﷺ) said: "Whoever is killed defending himself against injustice, he is a martyr."
Source: sunnah.com
Other translations
Arabic
أَخْبَرَنَا الْقَاسِمُ بْنُ زَكَرِيَّا بْنِ دِينَارٍ، قَالَ حَدَّثَنَا سَعِيدُ بْنُ عَمْرٍو الأَشْعَثِيُّ، قَالَ حَدَّثَنَا عَبْثَرٌ، عَنْ مُطَرِّفٍ، عَنْ سَوَادَةَ بْنِ أَبِي الْجَعْدِ، عَنْ أَبِي جَعْفَرٍ، قَالَ كُنْتُ جَالِسًا عِنْدَ سُوَيْدِ بْنِ مُقَرِّنٍ فَقَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " مَنْ قُتِلَ دُونَ مَظْلَمَتِهِ فَهُوَ شَهِيدٌ " .
sunnah.com