Sayyiduna Sahl bin Sa'd (may Allah be pleased with him) said: "On the day of Uhud the helmet was broken on the head of the Messenger of Allah (peace and blessings be upon him), his (peace and blessings be upon him) incisor (ruba'i) tooth was broken, and his (peace and blessings be upon him) face was wounded. The daughter of the Messenger of Allah (peace and blessings be upon him), Sayyidah Fatimah (may Allah be pleased with her), was washing the blood from it, and Sayyiduna Ali bin Abi Talib (may Allah be pleased with him) was bringing her water. When the water touched the wound, the blood flowed even more and would not stop, until Sayyidah Fatimah (may Allah be pleased with her) took a piece of a mat, burned it until it became ash, then applied it to the wound, and the blood stopped."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 5768