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كتاب فضائل أصحاب النبى صلى الله عليه وسلم
62  
Companions of the Prophet
(28)
Chapter: Narration about Mu'awiya رضي الله عنه
(28)
باب ذِكْرُ مُعَاوِيَةَ رضى الله عنه
Sahih al-Bukhari 3764

Narrated Ibn Abu Mulaika:

Muawiya offered one rak`a witr prayer after the `Isha prayer, and at that time a freed slave of Ibn `Abbas was present. He (i.e. the slave) went to Ibn `Abbas (and told him that Muawiya offered one rak`a witr prayer). Ibn `Abbas said, "Leave him, for he was in the company of Allah's Messenger (ﷺ)."

حَدَّثَنَا الْحَسَنُ بْنُ بِشْرٍ، حَدَّثَنَا الْمُعَافَى، عَنْ عُثْمَانَ بْنِ الأَسْوَدِ، عَنِ ابْنِ أَبِي مُلَيْكَةَ، قَالَ أَوْتَرَ مُعَاوِيَةُ بَعْدَ الْعِشَاءِ بِرَكْعَةٍ وَعِنْدَهُ مَوْلًى لاِبْنِ عَبَّاسٍ، فَأَتَى ابْنَ عَبَّاسٍ فَقَالَ دَعْهُ، فَإِنَّهُ صَحِبَ رَسُولَ اللَّهِ صلى الله عليه وسلم‏.‏
Reference : Sahih al-Bukhari 3764
In-book reference : Book 62, Hadith 109
USC-MSA web (English) reference : Vol. 5, Book 57, Hadith 108
  (deprecated numbering scheme)