Musnad Ahmad 30:1966

Aswad narrated to us, Sharik narrated to us, from al-A'mash, from Abu Salih, from Abu Hurairah, from the Prophet (peace and blessings of Allah be upon him), who said: "Whoever is wounded in the way of Allah—and Allah knows best who is wounded in His way—the wound will come on the Day of Resurrection, its color being the color of blood, and its scent being the scent of musk."