Sahih Bukhari – Hadith No : 991

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

Hadith In Arabic Text :

وعن نافع، أن عبد الله بن عمر، كان يسلم بين الركعة والركعتين في الوتر، حتى يأمر ببعض حاجته‏.‏

Chapter : Witr Prayer – كتاب الوتر