The witr prayer is not obligatory like the prescribed prayers, but it is a sunnah established by the Messenger of Allah ﷺ.
حدثنا وكيع حدثنا سفيان عن أبي إسحاق عن عاصم بن ضمرة
الوتر ليس بحتم مثل الصلاة ولكنه سنة سنها رسول الله ﷺ
Its isnad is sahih, and in al-Muntaqa 1183 it is mentioned that Tirmidhi, Nasai, and Ibn Majah also narrated it.