Musnad AhmadChapter 5Hadith 616
Full Sharh — Musnad Ahmad 616
حَدَّثَنَا وَكِيعٌ، حَدَّثَنَا سُفْيَانُ، عَنْ أَبِي إِسْحَاقَ، عَنْ عَاصِمِ بْنِ ضَمْرَةَ، عَنْ عَلِيٍّ، رَضِيَ اللَّهُ عَنْهُ قَالَ الْوَتْرُ لَيْسَ بِحَتْمٍ مِثْلَ الصَّلَاةِ وَلَكِنَّهُ سُنَّةٌ سَنَّهَا رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ.
English Translation
It was narrated that ‘Ali (رضي الله عنه) said:: Witr is not an essential like regular prayer, but it is a Sunnah that was established by the Messenger of Allah (ﷺ).
Source
Musnad Ahmad(مسند أحمد)
Musnad 'Ali Ibn Abi Talib
Hadith Number
616