Musnad Ahmad 1013:33

Rab'i ibn Ibrahim narrated to us, Abd al-Rahman ibn Ishaq narrated to us, from Abu Hazim, that Sahl ibn Sa'd said: "I saw Fatimah, the daughter of the Messenger of Allah, may Allah bless him and grant him peace, on the day of Uhud. She burned a piece of a mat, then she took it and applied it to the wound of the Messenger of Allah, may Allah bless him and grant him peace, which was on his face. He said: And a shield containing water was brought, so she washed the blood from him."