Authentic Supplication Number 050.

Ibn 'Umar said that a man asked the Messenger of Allah  about the night prayer: So the Messenger of Allah  said: The night prayer is dual dual, then if one of you is worried about morning he would pray a single rak'ah, which would make that which he had prayed odd [in number]. Nafi` told that `Abdullah bin `Umar used to say tasleem between the single rak`ah, and the two rak`ahs in the Witr such that he could tend to some of his needs.

Reported in Saheeh 'Al-Bukhari #105 in the chapters of Witr in Volume 2 of Muhammad Muhsin Khan's translation.