Kuraib, the freed slave of Ibn Abbas (may Allah be pleased with them), narrates that he saw Muawiyah (may Allah be pleased with him) perform the Isha prayer, and then he did not pray anything except one rak'ah of Witr. Kuraib (may Allah have mercy on him) related this to Ibn Abbas (may Allah be pleased with them), so he said: "He has spoken the truth. O son! None of us knows more about this matter than Muawiyah (may Allah be pleased with him). This Witr can be one, or five, or more than seven. One may pray as many as he wishes."
Hadith Referenceمسند الإمام الشافعي / كتاب الصلاة / 394
Hadith Takhrijاسنادہ ضعیف: فان عتبہ بن محمد مقبول حیث یتابع ولم یتابع اخرجہ البیہقی: 24/3 (4457) ۔ وعبدالرزاق (4641) ۔ ورواہ البخاری من غیر ھذا الطریق، انظر صحیح البخاری، فضائل اصحاب النبی، باب ذکر معاویہ (3764)، (3765)۔