Umar bin Khattab gathered the people behind Ubayy bin Kaab, who would lead them in prayer for twenty nights, performing the qunut supplication only during the latter half. When the last ten nights arrived, Ubayy would withdraw and pray in his own house, and the people would say, "Ubayy has slipped away."
حدثنا شجاع بن مخلد حدثنا هشيم أخبرنا يونس بن عبيد
أن عمر بن الخطاب جمع الناس على أبي بن كعب فكان يصلي لهم عشرين ليلة ولا يقنت بهم إلا في النصف الباقي فإذا كانت العشر الأواخر تخلف فصلى في بيته فكانوا يقولون أبق أبي
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[Its chain is daif] Bayhaqi transmitted it (2/498) from the hadith of Abu Dawud through this route. Ayni said that it contains a break, since Hasan did not meet Umar bin Khattab (Sharh Sunan Abu Dawud, 5/343, no. 1399). He said, Nawawi said in Khulasah, "Both routes are daif."