Sayyiduna Ali (may Allah be pleased with him) said: Witr is not obligatory like the (fard) prayer, but it is Sunnah and do not abandon it.
Hadith Referenceسنن دارمي / من كتاب الصللاة / 1618
Hadith Gradingتحقیق (حسین سلیم أسد الدارانی):إسناده صحيح إلى علي، [مكتبه الشامله نمبر: 1620]
Hadith Takhrijیہ روایت سیدنا علی رضی اللہ عنہ پر موقوف اور صحیح ہے۔ دیکھئے: [أبوداؤد 1416] ، [ترمذي 453] ، [نسائي 1676] ، [أبويعلی 317]
Brief Explanation
(Commentary on Hadith 1617)
From all these narrations, it is understood that the obligatory prayers (fardh) are only five; apart from these, all others are Sunnah and voluntary (nafl) prayers. And, unlike the obligatory prayers, neither the witr prayer nor any other prayer is obligatory (wajib), as stated by Sayyiduna Ali radi Allahu anhu. However, one should not abandon the witr prayer, because the Noble Prophet sallallahu alayhi wa sallam never left the witr prayer, whether during travel or residence. Therefore, following the Messenger sallallahu alayhi wa sallam means to always be consistent in performing the witr prayer. If it is performed in the last part of the night, it is more virtuous, because the Prophet sallallahu alayhi wa sallam mostly performed it at the end of the night. And if it is performed after the ‘Isha prayer, that is also permissible.