Musnad Ahmad 1153:760

Al-Aswad ibn Amir narrated to us, he said: Shu'bah informed us, from Qatadah, from Zurarah ibn Awfa, from Sa'd ibn Hisham, from Aisha, she said: "When the Prophet, peace and blessings of Allah be upon him, was ill or asleep, he would pray twelve rak'ahs during the day." She said: "And I never saw him stand [in prayer] for a whole night until the morning, nor did he fast a complete month consecutively, except for Ramadan." And she said: "The Messenger of Allah, peace and blessings of Allah be upon him, used to perform a deed and then establish it."