There is a Hadith in Imam Baihaqui’s Sunan e Sughra and Ma’arifatus Sunan:
عن السائب بن يزيد ، قال : كنا نقوم في زمان عُمَر بن الخطاب رضي الله عنه بعشرين ركعة والوتر-
Translation: Hadhrat Saib bin Yazid (May Allah be well pleased with him) says: In the era of Hadhrat Umar (May Allah be well pleased with him), we used to offer 20 Raka’at of Taraweeh and 3 Raka’at of Witr.
Allama Kamaaluddeen Muhammad, more famously known as Ibn Hamam (May Allah shower His mercy on him), the author of Fath Ul Qadeer writes after relating this Hadith:
Translation: Imam Nawawi (May Allah shower His mercy on him) has written in Khulasatul Ahkaam that the chain of narration of this Hadith is rigorously authenticated (Sahih).