´Ali narrated:` "Allah's Messenger would perform Al-Witr with three, reciting nine Surah from the Mufassal in them, reciting three Surah in each Rak'ah with Say: "Allah is One." At the end of them."Muhammad bin Sirin said: "They would perform Al-Witr with five, with three, and with one Rak'ah, and they considered all of that to be good."
Hadith Referenceسنن ترمذي / أبواب الوتر / 460
Hadith Gradingالألبانی:ضعيف جدا، المشكاة (1281) | زبیر علی زئی:(460) إسناده ضعيف, ھشام بن حسان مدلس و عنعن (د 443)