I heard the Messenger of Allah ﷺ say, "Whoever sets out in the cause of Allah and then dies or is killed is a martyr. Whether his horse or camel throws him and breaks his neck, or a venomous creature stings him, or he dies in his bed, or by any manner of death Allah wills, he is indeed a martyr and Paradise is his."
حدثنا عبد الوهاب بن نجدة حدثنا بقية بن الوليد عن ابن ثوبان عن أبيه يرد إلى مكحول إلى عبد الرحمن بن غنم الأشعري أن
سمعت رسول الله ﷺ يقول من فصل في سبيل الله فمات أو قتل فهو شهيد أو وقصه فرسه أو بعيره أو لدغته هامة أو مات على فراشه أو بأي حتف شاء الله فإنه شهيد وإن له الجنة
[Its chain is daif] Recorded by Hakim: 22/78, 79, from the hadith of Abdul-Wahhab bin Najdah, through this chain, and he graded it sahih according to the criteria of Muslim, but Dhahabi rejected this, saying, "Abdul-Rahman bin Ghanm was not, I think, reached by Makhul, and Baqiyyah is a mudallis who did not explicitly state hearing it in the chained transmission."