20 Raka’at of Taraweeh have beeen mentioned in various Hadith that in the era of Hadhrat ‘Umar, Hadhrat ‘Uthman and Hadhrat ‘Ali (May Allah be well pleased with them), 20 Raka’at of Taraweeh was offered.
This is that blessed era in which most of the Companions were present and people would come from all over the world to them and learn the teachings of Islam. They would value the customs and the practices of the Companions.
In the era of Hadhrat ‘Umar (May Allah be well pleased with him), people would offer 20 Raka’at of Taraweeh. As mentioned in this Hadith:
Translation: It has been narrated on the authority of Hadhrat Yazid bin Rooman (May Allah be well pleased with him) that he said: In the era of Hadhrat ‘Umar bin Khattab (May Allah be well pleased with him) people used to offer 23 Raka’at (20 Raka’at of Taraweeh and 3 Witr).
Allama Badruddin ‘Aini (May Allah shower His mercy on him) writes in the interpretation of this Hadith:
Translation: Allama Ibn Abdul Barr (May Allah shower His mercy on him) said: "23 Raka’at means 20 Raka’at of Taraweeh and 3 of Witr." (Umdatul Qari Sharh Sahih Bukhari, Kitab Ut Taraweeh, Vol 8, Pg No: 245)
Hadhrat Umar’s (May Allah be well pleased with him) command for offering 20 Raka’at of Taraweeh
Hadhrat ‘Umar ordered the Imams who led the Salaat to lead the people in 20 Raka’at of Taraweeh. There is a Hadith in Musannaf Ibn Abi Shaiba:
Translation: It has been narrated on the authority of Hadhrat Yahya bin Sa‘eed that Hadhrat Umar (May Allah be well pleased with him) commanded a person to offer 20 Raka’at of Taraweeh. (Musannaf Ibn Abi Shaiba, Vol 2, Pg No: 285, Chapter No: 227, Hadith No: 3; Tuhfatul Ahwazi, Bab Ma Ja'a Fi Shahri Ramadhan)