Hadith: Witr is not incumbent like the status of the obligatory prayers, but it is a Sunnah that the Messenger of Allah (may Allah's peace and blessings be upon him) started practicing

عن علي رضي الله عنه قال: «الوِتر ليس بِحَتْمٍ كَهَيْئَةِ الصلاة المَكتوبة، ولكن سُنَّة سَنَّها رسول الله صلى الله عليه وسلم ».
[صحيح] - [رواه الترمذي و أحمد و النسائي و ابن ماجه]

‘Ali (may Allah be pleased with him) said: "Witr is not incumbent like the status of the obligatory prayers, but it is a Sunnah that the Messenger of Allah (may Allah's peace and blessings be upon him) started practicing."
[Authentic hadith] - [Narrated by Ibn Majah - Narrated by At-Termedhy - An-Nasaa’i - Narrated by Ahmad]

Explanation

The Hadīth means that performing the Witr prayer is not obligatory like the obligatory five daily prayers, but it is a Sunnah that the Messenger of Allah (may Allah's peace and blessings be upon him) established. This last part of the Hadīth stresses the fact that the Witr prayer is desirable and recommended only, and the Messenger of Allah (may Allah's peace and blessings be upon him) performed it without making it obligatory upon us.