Hammad bin Zayd حماد بن زيد بن درهم الأزدي الأزرق · The Book on Al-Witr

he asked Ibn Umar about the length of the two Rak'ah (before) Al-Fajr. He said: "The Prophet would pray two and two during the night, and he would perform Al-Witr with one Rak'ah. And he would pray two Rak'ah while he was hearing the Adhan ."