Answer
(Fatwa: 1729/D=243/K=1430)
Sayyidna Ibn Abbas (رضی اللہ عنہ) narrated that the Messenger of Allah (صلی اللہ علیہ وسلم) used to perform twenty rak?ah tarawih in Ramadan. (Musannaf Ibn Abi Shaybah 2:166) The companions also used to perform twenty rak?ah tarawih in Ramadan.
Sayyinda Ubay bin Ka?ab used to lead people in twenty rak?ah tarawih at Medinah Munawwarah, then he used to lead the three rak?ah of witr salah. (Musannaf Ibn Abi Shaybah 2:165)
It is reported in hadith books that Muslims used to perform twenty rak?ah tarawih in the caliphate of Sayyidna Umar and Sayyidna Usman (رضی اللہ عنھما). (al-Sunan al-Kubra of Bayhaqi)
Therefore, the scholars of Fiqh like Imam Azam Abu Hanifah, Imam Malik, Imam Shafi?i, Imam Ahmad bin Hanbal and other scholars have unanimously agreed that tarawih is at least twenty rak?ah, (there is an opinion of Imam Malik which says that tarawih is more than 20), but none of the Four Imams regard it less than twenty. And the entire Ummah across the world acts upon the same ruling for centuries. According to Imam Azam Abu Hanifah, twenty rak?ah tarawih is sunnah ghair muakkadah; therefore it should be performed so. If only eight rak?ah tarawih is offered in your mosque, you should perform 12 remaining rak?ah at home and then perform witr salah.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband