It is narrated from Hazrat Abu Huraira (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: There are five types of martyrs. Dying due to plague is martyrdom, dying due to a stomach disease is martyrdom, drowning in water is martyrdom, dying by falling is martyrdom, and being killed in the path of Allah (jihad) is also martyrdom.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 8305