Hadith #2537 (Sunan Ibn Majah)
Book: The Chapters on Jihad
Narrator(s): Abdur Rahman bin Mahdi عبد الرحمن بن مهدي, Abu Hurairah, Hyan bin Bstam al-Hdhly al-Bsry حيان بن بسطام, Saleem bin Hiyyan سليم بن حيان

“We hoped that when he died it would be as a martyr in the cause of Allah.” The Messenger of Allah (ﷺ) said: “In that case the martyrs of my nation would be few. Being killed in the cause of Allah is martyrdom; dying of the plague is martyrdom; when a pregnant woman dies in childbirth that is martyrdom; and dying of drowning, or burning, or of pleurisy, is martyrdom.”

Source: https://parallelquran.com/hadith/sunan-ibn-majah-2537/