Jami at Tirmidhi 453

Sufyan Ath-Thawri and others reported from Abu Ishaq, from Asim bin Damrah, that : Ali said: Al-Witr is not incumbent like the status of the obligatory prayers, but it is a Sunnah which Allah's Messenger practiced. ..

Abu Hurairah narrated: Allah's Messenger ordered me to perform Al-Witr before sleeping. ..

Masruq narrated that : he asked Aishah about the Witr of the Prophet. She said: He would perform Witr during all of the night; (either) its beginning, its middle, or its end. So when he died, his Witr ended, during the approachof As-Sahar. ..

Umm Salamah narrated: The Prophet would perform Witr with thirteen [Rak'ah]. When he was older and became weak he performed Witr with seven. ..

Umm Salamah narrated: The Prophet would perform Witr with thirteen [Rak'ah]. When he was older and became weak he performed Witr with seven. ..

Aishah narrated: The night prayer of Allah's Messenger was thirteen Rak'ah, five of which were his Witr, not sitting in any of them except at the end of them. When the Mu'adh-dhin called the Adhan he would stand to perform two light (Rak'ah). ..