مُوَطَّأُ مَالِكٍ
Muwatta Malik 274
Tahajjud
وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ نَافِعٍ، أَنَّ عَبْدَ اللَّهِ بْنَ عُمَرَ، كَانَ يُسَلِّمُ بَيْنَ الرَّكْعَتَيْنِ وَالرَّكْعَةِ فِي الْوِتْرِ حَتَّى يَأْمُرَ بِبَعْضِ حَاجَتِهِ .
Yahya related to me from Malik from Nafi that Abdullah ibn Umar used to say the taslim between the two rakas and the one raka of witr so that he could order something he needed.
Arabic/English book reference: Book 7, Hadith 20