Musnad Ahmad 1153:567

Abu al-Yaman narrated to us, he said: Shu'ayb informed us, from al-Zuhri, he said: Sa'id ibn Khalid ibn 'Amr ibn 'Uthman ibn 'Affan informed me—and I was narrating these hadiths to him—that he asked 'Urwah ibn al-Zubayr about what the fire has touched. 'Urwah ibn al-Zubayr said: I heard 'Aishah, the wife of the Prophet, may Allah bless him and grant him peace, saying: The Messenger of Allah, may Allah bless him and grant him peace, said: "Perform ablution from what the fire has touched."