Sunan Ibn Majah, Chapter: The Chapters on Jihad

from his father, that his grandfather fell sick and the Prophet (saw) came to visit him. One of his family members said: "We hoped that when he died it would be as a martyr in the cause of Allah." The Messenger of Allah (saw) 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."