قَالَ الْحَارِثُ بْنُ مِسْكِينٍ قِرَاءَةً عَلَيْهِ وَأَنَا أَسْمَعُ، عَنْ سُفْيَانَ، عَنِ الزُّهْرِيِّ، عَنْ عَطَاءِ بْنِ يَزِيدَ، عَنْ أَبِي أَيُّوبَ، قَالَ مَنْ شَاءَ أَوْتَرَ بِسَبْعٍ وَمَنْ شَاءَ أَوْتَرَ بِخَمْسٍ وَمَنْ شَاءَ أَوْتَرَ بِثَلاَثٍ وَمَنْ شَاءَ أَوْتَرَ بِوَاحِدَةٍ وَمَنْ شَاءَ أَوْمَأَ إِيمَاءً ‏.‏

Sufyan narrated from Az-Zuhri, from 'Ata bin Yazid, from Abu Ayyub, who said: "Whoever wants to pray witr with seven (rak'ahs) let him do so, and whoever wants to pray witr with five (rak'ahs) let him do so, and whoever wants to pray witr with three rak'ahs, let him do so; and whoever wants to pray witr with one rak'ah, let him do so, and wants to do so gesturing, let him do so.'" Translation Not Available

Book Ref: Sunan An Nisai Book 20 Hadith 1713
Web Ref:  Sunan An Nisai Vol 2 Book 20 Hadith 1714