Musnad Ahmad 1153:305

Ibn Numayr narrated to us, from Talhah ibn Yahya, who said: Aisha bint Talhah narrated to me, from Aisha, "That the Messenger of Allah (peace and blessings of Allah be upon him) used to engage in physical intimacy (mubasharah) while he was fasting, then he would place a garment between himself and her, meaning the private part."