Al-Hasan (may Allah have mercy on him) says that Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) gathered the people behind Sayyiduna Ubayy bin Ka'b (may Allah be pleased with him). He would lead them in tarawih for twenty nights, and would recite the qunut only in the remaining half (the last fifteen days). When the last ten days came, Sayyiduna Ubayy bin Ka'b (may Allah be pleased with him) would pray in his house, and the people would say: Ubayy has run away.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4630