Sunan Ibn Majah, Chapter: The Chapters on Medicine

"The Messenger of Allah (saw) was wounded on the Day of Uhud. His molar was broken and his helmet was crushed on his head. Fatimah was washing the blood from him and Ali was pouring water on him from a shield. When Fatimah realized that the water was only making the bleeding worse, she took a piece of a mat and burnt it, and when it had turned to ashes, she applied it to the wound to stop the bleeding.