From Sahih Bukhari (Hadith 5722):
Narrated Sahl bin Sa`d As-Sa`idi:When the helmet broke on the head of the Prophet (ﷺ) and his face became covered with blood and his incisor tooth broke (i.e. during the battle of Uhud), `Ali used to bring water in his shield while Fatima was washing the blood off his face. When Fatima saw that the bleeding increased because of the water, she took a mat (of palm leaves), burnt it, and stuck it (the burnt ashes) on the wound of Allah's Apostle, whereupon the bleeding stopped
Reference: Bukhari 5722