Al-A'mash (may Allah have mercy on him) narrates from some of his associates that Abdullah bin Mas'ud (may Allah be pleased with him) said: The witr is seven or five, and not fewer than three.
It has also been reported from al-A'mash from Ibrahim, who said: Abdullah bin Mas'ud (may Allah be pleased with him) said it; but that is munqati' (with a broken chain) and mawquf (stopping at the Companion).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4813