[The Ruling on Washing One Killed in Self-Defense]

Answer—and Allah is the One who grants success: The original rule is the obligation to wash the deceased Muslim. Exempted from this are the martyrs, by his saying (May Allah bless him and his family and grant them peace) regarding the martyrs of Uḥud: “Wrap them in their garments with their blood, for there is no wound inflicted in the path of Allah but that it will come on the Day of Resurrection with the color of blood and the fragrance of musk,” and the like. There is no disagreement about this—meaning one killed in battle—except from al-Baṣrī and Rabīʿah.
In al-Majmūʿ from the Prophet (May Allah bless him and his family and grant them peace): “If the martyr dies the same day or the next, bury him in his clothes; but if he remains for days until his wounds change, then he is washed.”
Once this is understood, know that the evidences for not washing the martyr indicate non-washing for the martyr slain while striving in the path of Allah. As for one killed in a town wrongfully, or while defending his person or property, no evidence has come for not washing them except by analogy with the battle martyr—and that analogy is invalid. This is because his saying (May Allah bless him and his family and grant them peace), “for there is no wound inflicted in the path of Allah, but will come on the Day of Resurrection … etc,” indicates that the effective cause is being killed in the path of Allah. One killed defending himself or another, whether in a town or elsewhere, is not killed in the path of Allah (in the specific legal sense of combat); rather, he is killed in the path of defending himself, his property, or another. The effective cause is not merely his being termed a “martyr”; otherwise the ruling would extend to the one who dies of abdominal illness (al-mabṭūn), the woman who dies in childbirth, and others whom the Messenger (May Allah bless him and his family and grant them peace) named as martyrs—yet the ruling does not extend to them.
Source : Min Thimār al-ʿIlm wa al-Ḥikmah vol.1