(30) CHAPTER. There are seven martyrs other than those who are killed in Jihad (i.e., eight).
Narrated Abu Huraira: Allah's Apostle said, Five are regarded as martyrs: They are those who die because of plague, Abdominal disease, drowning or a falling building etc., and the martyrs in Allah's Cause.
Narrated Anas bin Malik: The Prophet said, Plague is the cause of martyrdom of every Muslim (who dies because of it).