Qatada reported,

Saad bin Hisham said, "I divorced my wife and came to Madinah to sell a property I owned there, so that I could buy weapons with the proceeds and go out to fight. I met a group of the Companions of the Prophet ﷺ, and they said, 'Six men among us wanted to do exactly that, and the Prophet ﷺ forbade them, saying, "You have in the Messenger of Allah an excellent example" [Ahzab 33:21].'Then I went to Ibn Abbas and asked him about the witr of the Prophet ﷺ. He said, "Shall I direct you to the person who knows most about the witr of the Messenger of Allah ﷺ? Go to Ayesha ."So I set out to her, and I asked Hakeem bin Aflah to come with me. He refused at first, but I pressed him earnestly, and he went along with me. We asked permission to enter upon Ayesha.She asked, "Who is this?"He replied, "Hakeem bin Aflah."She asked, "And who is with you?"He said, "Saad bin Hisham."She asked, "Hisham bin Amir, the one who was killed on the day of Uhud?"I said, "Yes."She said, "What an excellent man Amir was."I said, "Umm Muiminin, tell me about the character of the Messenger of Allah ﷺ."She replied, "Do you not read the Quran? The character of the Messenger of Allah ﷺ was the Quran."I said, "Tell me about standing in prayer at night."She asked, "Do you not read 'O you who is wrapped in garments' [Muzzammil 73:1]?"I said, "Yes, I do."She said, "The beginning of this surah was revealed, and the Companions of the Messenger of Allah ﷺ stood in prayer until their feet became swollen. Then the closing portion of it was withheld in heaven for twelve months, after which its final part came down, and standing at night became voluntary after having been an obligation."I said, "Tell me about the witr of the Prophet ﷺ."She said, "He used to pray witr with eight rakats, sitting only in the eighth. Then he would rise and pray one more rakat, sitting only in the eighth and the ninth, and giving the salam only in the ninth. Then he would pray two rakats while seated. That makes eleven rakats, my son. When he grew older and put on weight, he prayed witr with seven rakats, sitting only in the sixth and the seventh, and giving the salam only in the seventh. Then he would pray two rakats while seated, and that makes nine rakats, my son. The Messenger of Allah ﷺ never spent an entire night in prayer until morning, he never recited the whole Quran in a single night, and he never fasted a complete month apart from Ramadan. Whenever he performed a prayer, he kept it up regularly, and whenever sleep overcame his eyes during the night, he would pray twelve rakats during the day."Then I went back to Ibn Abbas and told him what she had said. He said, "By Allah, this is indeed the sound account. Were I on speaking terms with her, I would go to her and hear it from her directly, face to face."I said, "Had I known that you do not speak with her, I would not have related it to you."In another wording she said, "He would pray eight rakats, sitting in them only at the eighth. He would sit and remember Allah , then supplicate, then give the salam audibly enough for us to hear it. Then, after giving the salam, he would pray two rakats while seated, and then pray one rakat. That makes eleven rakats, my son. When the Messenger of Allah ﷺ grew older and put on weight, he prayed witr with seven, and prayed two rakats while seated after giving the salam." The rest is the same in meaning, up to the words "face to face."

حدثنا محمد بن بشار حدثنا يحيى بن سعيد عن سعيد عن قتادة بإسناده نحوه قال يصلي ثماني ركعات لا يجلس فيهن إلا عند الثامنة فيجلس فيذكر الله عز وجل ثم يدعو ثم يسلم تسليما يسمعنا ثم يصلي ركعتين وهو جالس بعدما يسلم ثم يصلي ركعة فتلك إحدى عشرة ركعة يا بني فلما أسن رسول الله ﷺ وأخذ اللحم أوتر بسبع وصلى ركعتين وهو جالس بعدما يسلم بمعناه إلى مشافهة