Musnad Ahmad 30:3717

'Abd al-Samad narrated to us, my father narrated to us, al-Husayn—meaning al-Mu'allim—narrated to us, from Yahya, 'Abd al-Rahman ibn 'Amr narrated to me that he heard al-Muttalib ibn 'Abd Allah ibn Hantab al-Makhzumi saying: Ibn 'Abbas said: "Shall I perform ablution because of food I find lawful in the Book of Allah, the Almighty and Majestic, because fire has touched it?" Abu Hurayrah gathered pebbles in his hands and said: "I bear witness, by the number of these pebbles, that the Messenger of Allah, peace and blessings of Allah be upon him, said: 'Perform ablution from what fire has touched.'"