The Messenger of Allah ﷺ used to pray nine rakahs for his witr, but when he grew heavy and put on weight he prayed seven, and he also prayed two rakahs while seated, reciting in them "When the earth is shaken" [Zalzalah 99:1] and "Say, you disbelievers" [Kafirun 109:1].
كان رسول الله ﷺ يوتر بتسع حتى إذا بدن وكثر لحمه أوتر بسبع، وصلى ركعتين وهو جالس، يقرأ فيهما: {إذا زلزلت} و {قل يأيها الكفرون}.
Ahmad (22313), Tabarani in Al-Kabir (8/332), Bayhaqi (3/33), and Muhammad bin Nasr in his book Al-Witr (55) all reported it through the route of Umara bin Zazan, who said, Abu Ghalib narrated to us, from Abu Umama, and he mentioned it.Imam Ahmad (22246), Tabarani, and Bayhaqi (3/33) all reported it through the route of Abdul-Samad, meaning Ibn Abdul-Warith, who said, my father narrated to us, from Abdul-Aziz bin Suhayb, from Abu Ghalib, from Abu Umama, and he mentioned it in abbreviated form, namely his statement, "He used to pray two rakats after Witr, sitting, reciting in them."Haythami said in Al-Majma (2/241), "Ahmad and Tabarani reported it, and the men of Ahmad's chain are trustworthy." I say, its chain is hasan on account of the discussion regarding Abu Ghalib, except that his hadith is hasan. As for Umara bin Zazan, there is minor discussion about him, but he has been corroborated. For this reason, it may be that he erred in narrating this hadith from Thabit, from Anas, who said, the Prophet ﷺ used to pray Witr with nine rakats, and when he grew old and heavy he prayed Witr with seven, and he prayed two rakats sitting, reciting in them Surah Rahman and Surah Waqiah. Anas said, and we used to recite the short surahs, "When the earth is shaken" [Zalzalah 99:1] and "Say, O disbelievers" [Kafirun 109:1], and similar ones.Ibn Khuzayma (1079) reported it through two routes from Umara bin Zazan, from Thabit, with this wording. However, he was not corroborated in this narration. For this reason Bayhaqi (3/33) said, "Umara bin Zazan differed from all the other narrators regarding what the Prophet ﷺ recited in these two rakats," and he related from Bukhari that he said, Umara bin Zazan sometimes becomes confused in his hadith.It has also been narrated from Anas bin Malik, that the Prophet ﷺ used to pray two rakats after Witr sitting, reciting in the first rakat Umm Quran and "When the earth is shaken" [Zalzalah 99:1], and in the second, "Say, O disbelievers" [Kafirun 109:1]. Bayhaqi (3/33) and others reported it from Baqiya bin Walid, from Utba bin Abu Hakeem, from Qatada, from Anas, and he mentioned it. Baqiya bin Walid is a mudallis and he narrated it using an ambiguous form of transmission, and Utba bin Abu Hakeem is daif. Bayhaqi found fault with it on account of Utba bin Abu Hakeem, and on account of Abu Ghalib, who appears in the hadith of Abu Umama.