Hadithcore
Mishkat al-Masabih, 1265

Abu Ayyub reported God’s Messenger as saying, “The <i>witr</i> is a duty for every Muslim, so if anyone wishes to observe it with five <i>rak'as</i> he may do so; if anyone wishes to observe it with three he may do so; and if anyone wishes to observe it with one he may do so.” Abu Dawud, Nasa’i and Ibn Majah transmitted it.

وَعَنْ أَبِي أَيُّوبَ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «الْوَتْرُ حَقٌّ عَلَى كُلِّ مُسْلِمٍ فَمَنْ أَحَبَّ أَنْ يُوتِرَ بِخَمْسٍ فَلْيَفْعَلْ وَمَنْ أَحَبَّ أَنْ يُوتِرَ بِثَلَاثٍ فَلْيَفْعَلْ وَمَنْ أَحَبَّ أَنْ يُوتِرَ بِوَاحِدَةٍ فَلْيَفْعَلْ» . رَوَاهُ أَبُو دَاوُد وَالنَّسَائِيّ وَابْن مَاجَه

References1 variant
In-Book Reference
Book 4, Hadith 680