It is narrated from Hazrat Abu Usaib (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: After me, Jibreel came bringing fever and plague. I kept the fever confined to Madinah itself and sent the plague towards Shaam (Syria). Now, for my Ummah, the plague is martyrdom and mercy, whereas for the disbelievers it is a punishment.
Hadith Referenceمسند احمد / أول مسند البصريين / 20767