Musnad Abu Ya'la al-Mawsili 163:2

Ibrahim ibn al-Hajjaj al-Sami narrated to us, Hammad narrated to us, from Muhammad ibn Ishaq, from his father, from al-Hasan ibn Abi al-Hasan, from Fatimah, daughter of the Messenger of Allah (ﷺ), that the Messenger of Allah (ﷺ) ate some meat from a bone in her house. Then Bilal came to him and informed him of the prayer, so he stood up to pray. I took hold of his garment and said, "O my father, will you not perform ablution?" He said, "From what should I perform ablution, O my daughter?" I said, "From what the fire has touched." The Messenger of Allah (ﷺ) then said, "Is the purest of your food not that which the fire has touched?"