بُلُوغُ الْمَرَامِ
Bulugh al-Maram 382
The Book of Prayer
وَعَنْ عَلِيٍّ - رضى الله عنه - قَالَ: قَالَ رَسُولُ اَللَّهِ - صلى الله عليه وسلم -{ أَوْتِرُوا يَا أَهْلُ اَلْقُرْآنَ, فَإِنَّ اَللَّهَ وِتْرٌ يُحِبُّ اَلْوِتْرَ } رَوَاهُ اَلْخَمْسَةُ, وَصَحَّحَهُ اِبْنُ خُزَيْمَةَ . [1] .
Narrated 'Ali bin Abi Talib (RA): Allah's Messenger (ﷺ) said: "O people of the Qur'an! Offer Witr (prayer), because Allah is Witr (One) and loves Witr." [Reported by al-Khamsah and Ibn Khuzaimah graded it Sahih (authentic)].
Sunnah.com reference: Book 2, Hadith 286