There is a Hadith in Imam Baihaqui's Sunan Kubra and in ‘Umdatul Qari, Sharh Sahih Bukhari:
Hadhrat Abu Abdur Rahman Sulami narrates on the authority of Hadhrat Ali (May Allah be well pleased with him), that in the month of Ramadhan, he (i.e. Hadhrat Ali) summoned the Huffaz (those who memorized the Holy Quran) and commanded one Hafidh to lead others in 20 Raka’at of Taraweeh.
(Sunan Kubra Lil Baihaqui, Hadith No: 4804; Zujajatul Masabeeh, Vol 1, Pg No: 366; Umdatul Qari Sharh Sahih Bukhari, Kitab Ut Tahajjud; Tuhfatul Ahwazi, Bab Maa Ja'a Fi Qiyami Shahri Ramadhan)
Command to offer Taraweeh with 5 breaks
There is a Hadith in Imam Baihaqui’s Sunan Kubra, in Musannaf Ibn Abi Shaiba, in Kanz Ul ‘Ummal, etc.
Translation: It has been narrated on the authority of Hadhrat Abul Husna (May Allah be well pleased with him) that Hadhrat Ali (May Allah be well pleased with him) commanded a Hafidh to lead the people in 20 Raka’at of Taraweeh with 5 breaks.
(Sunan Kubra Lil Baihaqui, Hadith No: 4805; Musannaf Ibn Abi Shaiba, Vol 2, Pg No: 285, Bab 227, Hadith No: 2; Kanzul Ummal, Kitab Us Salaat, Hadith No: 23474; Umdatul Qari Sharh Sahih Bukhari, Kitab Ut Taraweeh; Tuhfatul Ahwazi, Bab Ma Ja'a Fi Qiyami Shahri Ramadhan)
One narrator in the aforementioned Hadith’s chain of narration is ‘Amr Bin Qais. Allama Ibn Turkmani (May Allah shower His mercy on him) writes in Jawahir Un Naqi:
Translation: I think ‘Amr Bin Qais is ‘Amr Bin Qais Malai. Imam Ahmed, Hadhrat Yahya, Hadhrat Abu Hatim, Hadhrat Abu Zara‘a and other Imams and Muhadditheen have declared him reliable.
It is imperative to act upon the Sunnah of the first four caliphs
It has been established by these highly authoritative and reliable canons of Hadith that the First Four Caliphs not only offered 20 Raka’at of Taraweeh themselves but also commanded others to do so. In Islamic law, the practice of the caliphs has its own legal status. The Holy Prophet (Sallallahu alaihi wa sallam) has commanded the Ummah to adopt their Sunnah.
Translation: Bind yourself to my Sunnah and to the Sunnah of my Caliphs and hold fast to it with your teeth.
(Sunan Ibn Majah, Vol. 1, Pg No: 5, Hadith No: 42)
Muhaddith-e-Deccan Hadhrat Abul Hasanaat Hadhrat Syed Abdullah Shah Sahab Naqshbandi Qadri Hanafi (May Allah shower His mercy on him) writes:
Translation: A total of 20 Raka’at of Taraweeh is a Sunnah Maukkada (Compulsory Sunnah) because this one of those acts which have been regularly performed by the Caliphs and it has been mentioned that it is imperative to follow the Sunnah of the Caliphs also and the one who leaves them is a sinner. (Haashiya Zujajatul Masabeeh, Vol. 1, Pg. No. 366)