Musannaf Ibn Abi Shaybah

Hasan narrates that Ubayy led the people in prayer during the caliphate of Umar. He did not recite the Qunoot supplication in prayer until half of Ramadan had passed. When half of Ramadan had passed, he recited the Qunoot supplication after bowing (ruku‘). When the last ten days began, he left and separated himself from the people. Then, during the caliphate of Umar, Mu‘adh al-Qari used to lead them in prayer during the last ten days.