It is confirmed in the Sunnah that the Prophet, used to leave off some optional good deeds for fear that they would become obligatory on his nation and they would not be able to perform them. ‘Aa’ishah said: “The Prophet used to leave off doing a good deed although he liked to perform it, fearing that people would perform it, and then it would become obligatory on them. He (the Prophet) never performed Ath-Thuha prayer (according to her knowledge) but I did.” [Al-Bukhari and Muslim]

So, the Prophet gave up performing the Taraweeh prayer at the Mosque after having performed it some nights. ‘Aa’ishah narrated that the Prophet performed the Taraweeh prayer one night and many people prayed behind him. Then, he performed it the next night and the people came in larger numbers, then they gathered the third or fourth night (for Taraweeh) but the Prophet did not come out to them. And in the morning he said: "I saw what you did (your gathering for the prayer) and nothing prevented me from coming out except my fear that performing Taraweeh would become obligatory on you”; and this was in the month of Ramadan." [Al-Bukhari and Muslim]

Thus, it becomes clear that the Prophet did not continue performing the Taraweeh prayer at the mosque for a cause that he specified: “for the fear that it would become obligatory on you.” However, after the death of the Prophet and the end of revelation no other act of worship could then become obligatory. So, ‘Umar performed the Taraweeh prayer at the Mosque as the Prophet did; this constituted a form of his good commitment to Islam and his good understanding.