Sahih Muslim
The Book on Government (Kitab Al-Imara)
Book Number: 020 / Hadith Number: 4705
It has been narrated on the authority of Abu Huraira that the, Messenger of Allah (may peace be upon him) said: While a man walks along a path, finds a thorny twig lying on the way and puts it aside, Allah would appreciate it and forgive him The Holy Prophet (may peace be upon him) said: The martyrs are of five kinds: one who dies of plague; one who dies of diarrhoea (or cholera) ; one who is drowned; one who is buried under debris and one who dies fighting in the way of Allah.