It was narrated from Sa'd bin Hisham that:
He met Ibn 'Abbas and asked him about Witr. He said: Shall I not lead you to one who knows best among the people of the world about the witr of the Messenger of Allah (ﷺ)? He said: Yes. (Ibn Abbas) said: It is 'Aishah. So go to her and ask her (about witr) and then come back to me and tell me the answer that she gives you. So I went to Hakim bin Aflah and asked him to go accompany me to her. He said: I shall not go to her, for I told her not to say anything about these two (conflicting) groups, but she refused (to accept my advice) and went on (to participate in the conflict). I swore an oath, beseeching him (to take me to her). So he came with me and went unto her. She said to Hakim: Who is this with you? He said: He is Sa'd bin Hisham. She said: Which Hisham? He said: Ibn Amir. She supplicated for mercy for him and said: What a good man Amir was. He said: O Mother of the Believers, tell me about the character of the Messenger of Allah. She said: Don't you read the Qur'an? I said: Yes. She said The character of the Messenger of Allah (ﷺ) was the Qur'an. He said: I wanted to get up (and leave), then I thought of the Qiyam (night prayer) of the Messenger of Allah (ﷺ) and said: Tell me about the Qiyam of the Messenger of Allah (ﷺ). She said: Do you not recite this surah: O you wrapped in garments? I said: Yes. She said: Allah, the Mighty and Sublime, made Qiyam Al-Lail obligatory at the beginning of this surah, so the Messenger of Allah (ﷺ) and his companions prayed Qiyam Al-Lail for one year. Allah (SWT) withheld the latter part of this surah for twelve months, then he revealed the lessening (of this duty) at the end of this surah, so Qiyam Al-Lail became voluntary after it had been obligatory. I felt inclined to stand up (and not ask anything further), then I thought of the witr of the Messenger of Allah (ﷺ). I said: O Mother of the Believers, tell me about the witr of the Messenger of Allah (ﷺ). She said: We used to prepare his siwak and water for his ablution, and Allah (SWT) would wake him when He wished during the night. He would use the siwak, perform ablution, and then pray eight rak'ahs in which he would not sit until he reached the eighth one. Then he would sit and remember Allah (SWT) and supplicate, then he would say the taslim that we could hear. Then he would pray two rak'as sitting after uttering the taslim, then he would pray one rak'ah, and that made eleven rak'ahs, O my son! When the Messenger of Allah (ﷺ) grew older and put on weight, he prayed witr with seven rak'ahs, then he prayed two rak'ahs sitting down after saying the taslim, and that made nine rak'ahs. O my son, when the Messenger of Allah (ﷺ)offered a prayer, he liked to continue to offer it, and when sleep, sickness, or pain distracted him from praying Qiyam Al-Lail, he would pray twelve rak'ahs during the day. I am not aware of the Prophet of Allah (ﷺ) having recited the whole Qur'an during a single night, or praying through the whole night until morning, or fasting a complete month, except Ramadan. I went to Ibn 'Abbas and told him what she had said, and he said: She has spoken the truth. If I could go to her (and meet her face to face) I would so that she could tell me all of that verbally.