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كتاب الوتر
14  
Witr Prayer
(1)
Chapter: What is said regarding the Witr prayer
(1)
باب مَا جَاءَ فِي الْوِتْرِ
Sahih al-Bukhari 991

Nafi` told that `Abdullah bin `Umar used to say Taslim between (the first) two Rak`at and (the third) odd one in the Witr prayer, when he wanted to attend to a certain matter (during that interval between the Rak`at).

وَعَنْ نَافِعٍ، أَنَّ عَبْدَ اللَّهِ بْنَ عُمَرَ، كَانَ يُسَلِّمُ بَيْنَ الرَّكْعَةِ وَالرَّكْعَتَيْنِ فِي الْوِتْرِ، حَتَّى يَأْمُرَ بِبَعْضِ حَاجَتِهِ‏.‏
Reference : Sahih al-Bukhari 991
In-book reference : Book 14, Hadith 2
USC-MSA web (English) reference : Vol. 2, Book 16, Hadith 105
  (deprecated numbering scheme)