Musnad Ahmad 1153:1797

Isma'il narrated to us, he said: Ibn 'Awn informed us, from Ibrahim, from al-Aswad and Masruq, they both said: We came to 'Aisha, may Allah have mercy on her, to ask her about physical intimacy for the fasting person, but we felt shy, so we stood up before we asked her. We walked—I do not know how far—then we said: We came to ask her about a need, then we return before asking her? So we returned and said: "O Mother of the Believers, we came to ask you about something, but we felt shy, so we stood up." She said: "What is it? Ask about whatever appears to you." We said: "Did the Prophet, peace and blessings of Allah be upon him, engage in physical intimacy while he was fasting?" She said: "He used to do that, but he was more in control of his desire than you are."