Praise be to Allah.
Shaykh Ibn Jibrin (may Allah have mercy on him) said:
“It is proven in al-Sahih that the Prophet (peace and blessings of Allah be upon him) used to pray eleven rak`ahs at night in Ramadan and at other times, but he would make the recitation and other essential parts of the prayer so long that on one occasion he recited more than five juz in a single rak`ah, reciting slowly and carefully.
And it is proven that he would get up halfway through the night , or shortly before or after that, and he would carry on praying until it was close to dawn, so he would pray thirteen rak`ahs in approximately five hours. This requires making the recitation and other essential parts of the prayer lengthy.
And it is proven that when `Umar united the Companions in praying Tarawih, they would pray twenty rak`ahs, reciting approximately thirty verses of al-Baqarah in each rak`ah, i.e., roughly four or five pages, so they would recite Surah al-Baqarah in eight rak`ahs, and if they recited it in twelve rak`ahs they would think that it was short.
This is the Sunnah in Tarawih prayer : if the recitation is kept short then the number of rak`ahs is increased to forty-one rak`ahs, as some of the imams said. If a person wants to limit himself to eleven rak`ahs or thirteen rak`ahs, then he should lengthen the recitation and other essential parts of the prayer. There is no set number for Tarawih prayer , rather what is required is to pray in the time that will enable you to attain tranquillity and not rush, no less than an hour or so. Whoever thinks that this is too long is going against what has been narrated and no attention should be paid to him.” (Fatawa Islamiyyah, 2:157-157)
And Allah knows best.