Sunan Ibn Majah, Chapter: The Chapters on Medicine

from his father, that his grandfather said: "On the Day of Uhud, I recognized the one who wounded the face of the Messenger of Allah (saw), the one who was washing the blood from the face of the Messenger of Allah (saw) and treating him, and the one who was bringing the water in a shield, and with what the wound was treated until the bleeding stopped. The one who was carrying the water in the shield was Ali. The one who was treating the wound was Fatimah. When the bleeding would not stop, she burned a piece of a worn out mat and applied the ashes to it (the wound), then the bleeding stopped.