I asked about what Ibn Abu Amra died from, and they said it was the plague. Anas bin Malik then said, "The Messenger of Allah ﷺ said, 'The plague is martyrdom for every Muslim.'"
حدثنا عبد الصمد حدثنا ثابت حدثنا عاصم
سألت أنس بن مالك بما مات ابن أبي عمرة فقالوا بالطاعون فقال قال رسول الله ﷺ الطاعون شهادة لكل مسلم
Its isnad is sahih. Asim is Ibn Sulayman al-Ahwal, and Hafsa is the daughter of Sirin, and she is trustworthy. The hadith was narrated by Bukhari 4/29, Book of Jihad, "Martyrdom is Seven Besides Killing," and by Muslim 3/1522, no. 1916, in the Book of Leadership, "Explanation of the Martyrs."