Sahih Bukhari
Medicine
Volume: 007 / Book Number: 071 / Hadith Number: 630
Narrated 'Aisha:
(the wife of the Prophet) that she asked Allah's Apostle about plague, and Allah's Apostle informed her saying, "Plague was a punishment which Allah used to send on whom He wished, but Allah made it a blessing for the believers. None (among the believers) remains patient in a land in which plague has broken out and considers that nothing will befall him except what Allah has ordained for him, but that Allah will grant him a reward similar to that of a martyr."