Praying Tarawih in congregation in Ramadan is Sunnah and not a bid’ah (innovation)
Question

Is praying Tarawih in congregation considered to be a bid’ah (innovation), because it was not done at the time of the Prophet and the first one who established that was ‘Umar ibn al-Khattaab (may Allah be pleased with him)?
Praise be to Allah.The view that Tarawih prayer is a bid’ah is not valid. Rather we should ask whether it was one of the Sunnahs of ‘Umar ibn al-Khattaab, because it was not done at the time of the Prophet (peace and blessings of Allah be upon him) but it was done in ‘Umar’s time, or was it one of the Sunnahs of the Prophet (peace and blessings of Allah be upon him)? 
Some people claim that it was one of the Sunnahs of ‘Umar, and they base that on the fact that ‘Umar “commanded Ubayy ibn Ka’b and Tameem al-Daari to lead the people in praying eleven rak’ahs.” He went out the same night and saw the people praying, and he said, “What a good innovation this is.” This indicates that it had not previously been prescribed… 
But this opinion is da’eef (weak), and those who say this are ignoring the reports proven in al-Saheehayn and elsewhere, that the Prophet (peace and blessings of Allah be upon him)  “led his companions in praying for three nights, and on the third or fourth night he did not lead them, and he said: ‘I am afraid that it may be made obligatory upon you.’” This was narrated by al-Bukhaari (872). According to a version narrated by Muslim, “But I was afraid that prayer at night may be made obligatory upon you, and you would not be able to do it.” (1271).  So it is proven that Tarawih is part of the Sunnah of the Prophet (peace and blessings of Allah be upon him). The Prophet (peace and blessings of Allah be upon him) referred to the reason why he did not persist in it, which was the fear that it might become obligatory; he did not say that it is not prescribed. This fear no longer applied following the death of the Messenger (peace and blessings of Allah be upon him), because when he (peace and blessings of Allah be upon him) died, the revelation ceased and there was no longer any concern that it might become obligatory. Once the fear that it might become obligatory was no longer present, because the revelation had ceased, then the reason for not doing it was also removed, and so it was restored to its position of being Sunnah. 
See al-Sharh al-Mumti’ by Ibn ‘Uthaymeen, vol. 4, p. 78. 
It was narrated in al-Saheehayn from ‘Aa’ishah (may Allah be pleased with her) that the Messenger of Allah (peace and blessings of Allah be upon him) would forgo doing something that he liked to do lest the people do it and it become obligatory upon them. (Narrated by al-Bukhaari, 1060; Muslim, Salaat al-Musaafireen, 1174). 
Al-Nawawi said: This shows how kind he (peace and blessings of Allah be upon him) was and how compassionate towards his ummah. 
So there is no basis for saying that Tarawih prayer is not part of the Sunnah of the Messenger of Allah (peace and blessings of Allah be upon him), rather it is part of the Sunnah of the Prophet (peace and blessings of Allah be upon him), but he forsook it for fear that it may be made obligatory upon his ummah. When he died, this concern no longer applied. Abu Bakr (may Allah be pleased with him) was distracted by the wars against the apostates and his reign was short, lasting only two years. When the reign of ‘Umar came and the Muslims became secure and victorious, he commanded the people to gather together for Tarawih prayers in Ramadan, as they used to gather with the Prophet (peace and blessings of Allah be upon him). All that ‘Umar (may Allah be pleased with him) did was to go back to that Sunnah and revive it. And Allah is the Source of strength.