Al-Matalib al-'Aliyah 634 — Witr

It is narrated from Umm Abdullah that she saw the Mother of the Believers, Sayyidah Aishah (may Allah be pleased with her), praying behind the Maqam of Ibrahim; then she prayed one rak'ah of witr in which she recited Surah Ibrahim. And with the same chain it is narrated that she heard Sayyidah Aishah (may Allah be pleased with her) say: "When you hear the call (of Fajr), then pray one rak'ah to make the witr."
Imam Musaddad recorded this report in his Musnad. This narration provides scholarly evidence for the permissibility of a single rak'ah of witr and for the end of its time, namely that the time of witr lasts until the adhan or call of Fajr. In its chain are Umm Shabib and her sister Umm Abdullah, who are among the mastur (narrators whose status is unknown).