Musnad Ahmad 1153:107

Sufyan narrated to us, from Ibn Abi Labid, from Abu Salamah: I said to Aisha, "O Mother, tell me about the prayer of the Messenger of Allah (peace and blessings of Allah be upon him)." She said, "His prayer in Ramadan and other than it was the same: thirteen rak'ahs, including the two rak'ahs of Fajr." I said, "Tell me about his fasting." She said, "He would fast until we would say, 'He has fasted,' and he would break his fast until we would say, 'He has broken his fast.' I never saw him fast a month more than his fasting in Sha'ban; he used to fast it, except for a little."