Hadith 4:482
'Abdah ibn Sulayman narrated to us, from Sa'id, from Qatadah, that the Prophet, may Allah bless him and grant him peace, said to a man who had intercourse with his wife during Ramadan: "If your back has broken [the fast], then do not let your stomach break [the fast]."
حدثنا عبدة بن سليمان عن سعيد عن قتادة أن النبي صلى الله عليه وسلم قال لرجل وقع على أهله في رمضان إن كان فجر ظهرك فلا يفجر بطنك