Musnad Ahmad 30:3739

Abdullah ibn al-Walid narrated to us, Sufyan narrated to us, from al-A'mash, from Dhakwan, from Abu Hurairah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "No servant is wounded in the way of Allah—and Allah knows best who is wounded in His way—but that his wound will come on the Day of Resurrection with its color being the color of blood, and its scent being the scent of musk."