It was said to Sayyiduna Ibn Abbas (may Allah be pleased with them both): Sayyiduna Mu'awiyah (may Allah be pleased with him) prayed witr with one rak'ah. He said: "Leave aside (objecting to) Mu'awiyah, for he has had the companionship of the Prophet (peace and blessings be upon him)."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11201