Sahih Bukhari Volume 4, Book 56, Hadith Number 680.

Narated By ‘Aisha : (The wife of the Prophet) I asked Allah’s Apostle about the plague. He told me that it was a Punishment sent by Allah on whom he wished, and Allah made it a source of mercy for the believers, for if one in the time of an epidemic plague stays in his country patiently hoping for Allah’s Reward and believing that nothing will befall him except what Allah has written for him, he will get the reward of a martyr.”