Narrated AbuMalik al-Ash'ari: AbuMalik heard the Messenger of Allah (ﷺ) say: He who goes forth in Allah's path and dies or is killed is a martyr, or has his neck broken through being thrown by his horse or by his camel, or is stung by a poisonous creature, or dies on his bed by any kind of death Allah wishes is a martyr and will go to Paradise.
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا عَبْدُ الْوَهَّابِ بْنُ نَجْدَةَ، حَدَّثَنَا بَقِيَّةُ بْنُ الْوَلِيدِ، عَنِ ابْنِ ثَوْبَانَ، عَنْ أَبِيهِ، يَرُدُّ إِلَى مَكْحُولٍ إِلَى عَبْدِ الرَّحْمَنِ بْنِ غُنْمٍ الأَشْعَرِيِّ أَنَّ أَبَا مَالِكٍ الأَشْعَرِيَّ، قَالَ سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ " مَنْ فَصَلَ فِي سَبِيلِ اللَّهِ فَمَاتَ أَوْ قُتِلَ فَهُوَ شَهِيدٌ أَوْ وَقَصَهُ فَرَسُهُ أَوْ بَعِيرُهُ أَوْ لَدَغَتْهُ هَامَّةٌ أَوْ مَاتَ عَلَى فِرَاشِهِ أَوْ بِأَىِّ حَتْفٍ شَاءَ اللَّهُ فَإِنَّهُ شَهِيدٌ وَإِنَّ لَهُ الْجَنَّةَ " .
sunnah.com