The Messenger of Allah ﷺ said, "The night prayer is two by two. When you fear the approach of dawn, pray a single rakah as witr, which will make all your prayers odd-numbered."Abdullah used to perform witr with a single rakah.
حدثنا زيد بن يحيى الدمشقي حدثنا عبد الله بن العلاء سمعت سالم بن عبد الله يقول سمعت
قال رسول الله ﷺ صلاة الليل مثنى مثنى فإذا خفت الفجر فأوتر بركعة توتر لك صلاتك قال وكان عبد الله يوتر بواحدة
Its isnad is sahih. Zayd bin Yahya bin Ubayd Dimashqi is trustworthy, one of the teachers of Ahmad. Ahmad, Ajli, Daraqutni, and others affirmed his trustworthiness. Abu Ali Nisaburi said, "Trustworthy and reliable." Bukhari included his biography in Kabir 2/1/3273.This hadith repeats the one before it with similar wording. His statement, "If you fear Fajr," is what is established in H and K, while in M it reads, "If you fear dawn." In a marginal copy of K it reads "dawn," and in a marginal copy of M it reads, "If you fear Fajr."