Musnad Ahmad 529:14

Al-Hakam ibn Nafi’ narrated to us, Isma’il ibn ‘Ayyash narrated to us, from Damdam ibn Zur’ah, from Shurayh ibn ‘Ubayd, from ‘Utbah ibn ‘Abd al-Sulami, from the Prophet, peace and blessings of Allah be upon him, who said: "The martyrs and those who died of the plague will come. The people of the plague will say: 'We are martyrs.' It will be said: 'Look, if their wounds are like the wounds of the martyrs, bleeding blood that smells of musk, then they are martyrs.' And they will find them to be so."