Ibn ‘Abbas, on being asked whether he approved of the Commander of the Faithful, Mu'awiya, using only one rak'a in the witr, replied, “He is right; he is versed in the law.” In a version Ibn Abu Mulaika said that Mu'awiya observed a witr after the evening prayer with one rak'u when a client of Ibn ‘Abbas was with him. He went to Ibn ‘Abbas and told him, but he replied, “Leave him alone, for he was a companion of the Prophet.” Bukhari transmitted it.
Hadith Referenceمشكوة المصابيح / كتاب الصلاة / 1277
Hadith Gradingالألبانی:صَحِيح | زبیر علی زئی:صحيح
Hadith Takhrij´تحقيق و تخريج: محدث العصر حافظ زبير على زئي رحمه الله` «رواه البخاري (3765)»