Nasai

Umm al-Mu’minin Umm Salamah (may Allah be pleased with her) says: The Prophet (peace and blessings of Allah be upon him) used to pray thirteen rak‘ahs of Witr, but when he became old and weak, he started praying seven rak‘ahs. © Imam Tirmidhi says:
1- The hadith of Umm Salamah (may Allah be pleased with her) is Hasan (good).
2- In this chapter, there is also a narration from ‘A’ishah (may Allah be pleased with her).
3- From the Prophet (peace and blessings of Allah be upon him), Witr with thirteen, eleven, nine, seven, five, three, and one (rak‘ah) are all narrated.
4- Ishaq bin Ibrahim (Ibn Rahwayh) says: This narration that the Prophet (peace and blessings of Allah be upon him) used to pray thirteen rak‘ahs of Witr means that he used to pray Tahajjud (Qiyam al-Layl) along with Witr, making thirteen rak‘ahs, so in this, Qiyam al-Layl (Tahajjud) is also called Witr. He has also narrated a hadith from ‘A’ishah (may Allah be pleased with her) in this regard, and has taken evidence from the statement of the Prophet (peace and blessings of Allah be upon him): “O people of the Qur’an! Pray Witr.” Ibn Rahwayh says that by this, the Prophet (peace and blessings of Allah be upon him) meant Qiyam al-Layl, and Qiyam al-Layl is only for those who believe in the Qur’an (not for followers of other religions).