Musnad Ahmad 32:577

'Abd al-Samad narrated to us, Thabit narrated to us, 'Asim narrated to us, from Hafsah, who said: Anas ibn Malik asked, "Of what did the son of Abu 'Amrah die?" They said, "Of the plague." He said: The Messenger of Allah, may Allah bless him and grant him peace, said: "The plague is martyrdom for every Muslim."