Assalamu alaykum. I read a hadith and would like to know the authenticity of the hadith and narrators. Saaib bin Yazeed (may Allaah be pleased with him) narrated, “During the Caliphate of Umar (may Allaah be pleased with him), we used to pray 8 rak’aahs (units of prayer) (of Taraweeh).” [Sunan Sa’eed bin Mansoor with reference from Al-Haawi lil Fatawaa by As-Suyuti: 1/349.] May Allaah reward you.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His Slave and Messenger.

The report narrated on the authority of As-Saa’ib ibn Yazeed says that they used to perform eleven rakʻahs (in the Taraaweeh prayer during the caliphate of 'Umar ). We did not find any reference to this report suggesting that they used to perform eight rakʻahs as the questioner mentioned. Imaam Maalik and others cited that Muhammad ibn Yoosuf narrated on the authority of As-Saa'ib ibn Yazeed that he said, "ʻUmar ibn Al-Khattaab ordered Ubayy ibn Kaʻb and Tameem Ad-Dayri (Ad-Daari) to lead the people in eleven rakʻahs as night prayer (in Ramadaan)." [Al-Muwattaa’]

This report has an authentic chain of narration as a group of hadeeth scholars declared it saheeh (sound). For instance, Al-Albaani said, "The chain of narration of this report is quite saheeh. As-Saa’ib ibn Yazeed was a young Companion, and Muhammad ibn Yoosuf was a trustworthy reporter accepted by Al-Bukhari and Muslim, and he was related to As-Saa’ib ibn Yazeed..."

However, some scholars held that the number 'eleven' in this report was, actually, a mistake on part of the reporter and that the other relevant versions stated that the correct number was twenty-one, not eleven. Ibn ʻAbd Al-Barr said:

"This is what Maalik said about this report, that they used to perform eleven rakʻahs, and other hadeeth scholars narrated reports stating that the number was twenty-one; none but Imaam Maalik narrated the report stating that the number was eleven. However, it is possible that they used to perform eleven rakʻahs when 'Umar first introduced the Sunnah of performing Taraaweeh prayers in congregation and then the length of the prayers was decreased to be twenty-one shorter rakʻahs (instead of long eleven ones) in which they used to recite less verses and prolong the rukooʻ (bowing) and sujood (prostration). Nevertheless, the opinion that I find most likely to be correct is that the number eleven was a mistake on part of the reporter...” [Al-Istithkaar: briefly excerpted]

Other scholars, on the other hand, held that the report suggesting that the number was eleven was not incorrect and that the reconciliation between the relevant reports on that issue underlined by Ibn ʻAbd Al-Barr is the correct opinion. Az-Zarqaani wrote in his commentary on Al-Muwatta’, "The number 'eleven' was not a mistake on part of the reporter; the relevant reports can be reconciled as suggested by Ibn ʻAbd Al-Barr; it is the same as the opinion of Al-Bayhaqi..."

Al-Haafith Ibn Hajar wrote:

"Scholars held different opinions in this regard; it was cited in Al-Muwatta’ on the authority of Muhammad ibn Yoosuf that As-Saa’ib ibn Yazeed said that the number of the rakʻahs was eleven. Saʻeed ibn Mansoor narrated the same report through another chain of narration with an addition reading, ‘They used to recite two hundred verses and lean on the sticks during the prayer given the prolonged qiyaam (standing position) in the prayer...’ Muhammad ibn Nasr Al-Marwazi narrated on the authority of Muhammad ibn Is-haaq that Muhammad ibn Yoosuf narrated that the number was thirteen rakʻahs. ʻAbd Ar-Razzaaq narrated a report through a different chain of narration on the authority of Muhammad ibn Yusuf saying that the number was twenty-one. Maalik, on the other hand, narrated on the authority of Yazeed ibn Khusayfah that As-Saa’ib ibn Yazeed said that the number was twenty rakʻahs. This is interpreted to be apart from the Witr prayer. It has been narrated on the authority of Yazeed ibn Roomaan that people used to perform twenty-three rakʻahs in night prayer during the reign of 'Umar. Muhammad ibn Nasr narrated on the authority of ʻAttaa’ that they used to perform twenty rakʻahs in Ramadaan and three rakʻahs as Witr. The possible reconciliation between those different narrations can be the difference of situations (they may have performed eleven rakʻahs on certain occasions and twenty-one on others); it may be according to the length of the prayer and the chapters recited in those rakʻahs. They may have been performing less rakʻahs with prolonged recitation and vice versa." [Fat-h Al-Baari]

Allaah Knows best.