In the Name of Allah, the Gracious, the Merciful
Imam al-Nawawi records in his book Meadows of the Righteous:
باب بيان جماعة من الشهداء في ثواب الآخرة يغسلون ويصلى عليهم بخلاف القتيل في حرب الكفار
Chapter clarifying a group of martyrs who will receive the reward of the Hereafter. They will be washed and prayed over, unlike those killed in war against the unbelievers.
Source: Riyāḍ al-Ṣāliḥīn 1/374
Abu Huraira reported: The Messenger of Allah, peace and blessings be upon him, said:
الشُّهَدَاءُ خَمْسَةٌ الْمَطْعُونُ وَالْمَبْطُونُ وَالْغَرِقُ وَصَاحِبُ الْهَدْمِ وَالشَّهِيدُ فِي سَبِيلِ اللَّهِ
The martyrs are five kinds: one who dies of plague, one who dies of stomach infection, one who drowns, one who dies under debris, and one who dies in the way of Allah Almighty.
Source: Ṣaḥīḥ al-Bukhārī 2829, Grade: Muttafaqun Alayhi
Abu Huraira reported: The Messenger of Allah, peace and blessings be upon him, said:
مَا تَعُدُّونَ الشَّهِيدَ فِيكُمْ
Who do you think is a martyr among you?
They said, “The one who is killed in the way of Allah.” The Prophet said:
إِنَّ شُهَدَاءَ أُمَّتِي إِذًا لَقَلِيلٌ
Verily, if that is so, then the martyrs among my nation are few.
They said, “O Messenger of Allah, then who are the martyrs?” The Prophet said:
مَنْ قُتِلَ فِي سَبِيلِ اللَّهِ فَهُوَ شَهِيدٌ وَمَنْ مَاتَ فِي سَبِيلِ اللَّهِ فَهُوَ شَهِيدٌ وَمَنْ مَاتَ فِي الطَّاعُونِ فَهُوَ شَهِيدٌ وَمَنْ مَاتَ فِي الْبَطْنِ فَهُوَ شَهِيدٌ
One who is killed in the way of Allah is a martyr, one who dies in the way of Allah is a martyr, one who dies of plague is a martyr, one who dies of stomach infection is a martyr, and one who dies from drowning is a martyr.
Source: Ṣaḥīḥ Muslim 1915, Grade: Sahih
Abdullah ibn Amr reported: The Prophet, peace and blessings be upon him, said:
مَنْ قُتِلَ دُونَ مَالِهِ فَهُوَ شَهِيدٌ
Whoever is killed defending his wealth is a martyr.
Source: Ṣaḥīḥ al-Bukhārī 2480, Grade: Muttafaqun Alayhi
Sa’id ibn Zayd reported: The Messenger of Allah, peace and blessings be upon him, said:
مَنْ قُتِلَ دُونَ مَالِهِ فَهُوَ شَهِيدٌ وَمَنْ قُتِلَ دُونَ دِينِهِ فَهُوَ شَهِيدٌ وَمَنْ قُتِلَ دُونَ دَمِهِ فَهُوَ شَهِيدٌ وَمَنْ قُتِلَ دُونَ أَهْلِهِ فَهُوَ شَهِيدٌ
Whoever is killed protecting his property is a martyr. Whoever is killed protecting his religion is a martyr. Whoever is killed protecting his life is a martyr. Whoever is killed protecting his family is a martyr.
Source: Sunan al-Tirmidhī 1421, Grade: Sahih
Abu Huraira reported: A man came to the Messenger of Allah, peace and blessings be upon him, and he said, “O Messenger of Allah, what do you think if a man comes to seize my wealth?” The Prophet said:
فَلَا تُعْطِهِ مَالَكَ
Do not give up your wealth.
The man said, “What if he fights me?” The Prophet said:
قَاتِلْهُ
Then fight him.
The man said, “What if he kills me?” The Prophet said:
فَأَنْتَ شَهِيدٌ
You will be a martyr.
The man said, “What do you think if I kill him?” The Prophet said:
هُوَ فِي النَّارِ
He will be in the Hellfire.
Source: Ṣaḥīḥ Muslim 140, Grade: Sahih
Success comes from Allah, and Allah knows best.