Sahih al-Bukhari, Hadith 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.
also referenced under: Book 14, Hadith 2 (In-Book) & Volume 2, Book 16, Hadith 105 (USC-MSA)