Sahih Bukhari Volume 4, Book 52, Hadith Number 274.

Narated By Abu Hazim : The people asked Sahl bin Sad As-Sa’ idi “With what thing (medicine) was the wound of Allah’s Apostle treated?” He replied, “There is none left (living) amongst the people who knows it better than. ‘Ali used to bring water in his shield and Fatima (i.e. the Prophet’s daughter) used to wash the blood off his face. Then a mat (of palm leaves) was burnt and its ash was inserted in the wound of Allah’s Apostle.”