Sunan Ibn Majah 1358

It was narrated that ‘Aishah said, and this is the Hadith of Abu Bakr. “During the period after he finished the ‘Isha’ prayer until the Fajr, the Prophet (ﷺ) used to pray eleven Rak’ah, saying the Salam after each two Rak’ah and praying Witr with one Rak’ah. He would prostrate for as long as it takes anyone of you to recite fifty Verses before he would raise his head. When the Mu’adh-dhin fell silent after the first Adhan for the Subh prayer, he would get up and pray two brief Rak’ah.”