Sa'd bin Hisham says: I came to Abdullah bin Abbas (may Allah be pleased with them both) and asked about the witr. He said: "Shall I tell you who, more than all people, knows about the witr of the Prophet (peace and blessings be upon him)?" The narrator says: I said: Who? He said: "Aishah (may Allah be pleased with her). Go to her and ask, and tell me too whatever answer she gives." I set out for Sayyidah Aishah (may Allah be pleased with her) and on the way took Hakim bin Aflah along with me. We came to Aishah (may Allah be pleased with her), sought permission and entered. Sayyidah Aishah (may Allah be pleased with her) asked: "Who is this?" I said: Hakim bin Aflah. Then Aishah (may Allah be pleased with her) asked: "Who is with you?" I said: Sa'd bin Hisham. She said: "Which Hisham?" I said: Ibn Amir. Sayyidah Aishah (may Allah be pleased with her) said: "Amir was a good man; he was struck down on the day of Uhud." I said: Mother of the Believers! Tell me about the character of the Messenger of Allah (peace and blessings be upon him). She said: "Have you not read the Qur'an?" I said: Of course. She (may Allah be pleased with her) said: "The character of the Messenger of Allah (peace and blessings be upon him) was the Qur'an itself."
Sa'd bin Hisham says: I intended to get up, then (another question) occurred to me. I said: O Mother of the Believers! Tell me about the night prayer of the Messenger of Allah (peace and blessings be upon him). She said: "Have you not read: 'O you wrapped in garments!' [Surah al-Muzzammil: 1]?" I said: Of course. She said: "At the beginning of this surah Allah made the night prayer obligatory, so the Prophet (peace and blessings be upon him) and his (peace and blessings be upon him) Companions (may Allah be pleased with them) stood in prayer for a year, so much that their feet became swollen. Allah held back (the closing part of) it in the heavens for twelve months, then He revealed the lightening at the end of this surah, and the night prayer became voluntary." The narrator says: I intended to get up, then the witr of the Prophet (peace and blessings be upon him) came to my mind. I said: O Mother of the Believers! Tell me about the witr of the Prophet (peace and blessings be upon him). She said: "We would keep ready the miswak and the water for ablution for the Prophet (peace and blessings be upon him), then Allah Almighty would wake him (peace and blessings be upon him) for whatever part of the night He wished. He (peace and blessings be upon him) would use the miswak and perform ablution, then he (peace and blessings be upon him) would pray nine rak'ahs, sitting only in the eighth rak'ah; he would supplicate to his Lord and send blessings upon His Prophet (peace and blessings be upon him), then he would stand up without saying the salam. Then he (peace and blessings be upon him) would pray the ninth rak'ah and sit, then praise Allah, send blessings upon His Prophet (peace and blessings be upon him) and supplicate, then he would say the salam loud enough for us to hear. After saying the salam he would pray two rak'ahs sitting. These are eleven rak'ahs. O my son! When the Prophet (peace and blessings be upon him) grew older and his body became heavy, he (peace and blessings be upon him) prayed seven rak'ahs of witr and prayed two rak'ahs after saying the salam. O my son! Whenever the Prophet (peace and blessings be upon him) prayed a prayer, he liked to be constant in it. If the night prayer of the Prophet (peace and blessings be upon him) was missed for some reason, he would pray twelve rak'ahs in the day. I do not know that the Prophet (peace and blessings be upon him) ever recited the whole Qur'an in one night, or stood in prayer the whole night, or fasted a complete month other than Ramadan." The narrator says: Then I came to Abdullah bin Abbas (may Allah be pleased with them both) and informed him, and he said: "She has spoken the truth." The beginning of Sa'd's affair was this; Ibn Bishr says: that is, the beginning of his affair was that he divorced his wife and travelled to Madinah to sell his property there and buy weapons and horses with it, and then to fight the Romans until he died. Then he met some people of his tribe, and they told him that six of their men had intended the same in the lifetime of the Prophet (peace and blessings be upon him), and the Prophet (peace and blessings be upon him) forbade them.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4638