Kurayb, the freed slave of Ibn Abbas (may Allah be pleased with them both), said: I saw Mu'awiyah (may Allah be pleased with him) pray Isha, then he prayed one rak'ah of witr, adding nothing to it. I informed Ibn Abbas (may Allah be pleased with them both), and Ibn Abbas (may Allah be pleased with them both) said: "None of us knows more than Mu'awiyah (may Allah be pleased with him). Witr may be one, five, seven or even more than that."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4794