Musnad Ahmad 1153:948

'Abd al-Wahhab ibn 'Ata narrated to us, he said: Hisham al-Dastawa'i informed us, from Hammad, from Ibrahim, from al-Aswad ibn Yazid, he said: I said to 'A'ishah: "Does the fasting person engage in physical intimacy—meaning with his wife?" She said: "No." I said: "Was the Messenger of Allah, may Allah bless him and grant him peace, not engaging in physical intimacy while he was fasting?" She said: "The Messenger of Allah, may Allah bless him and grant him peace, was the most capable of you in controlling his desire."