The following is a short list on what the scholars have said about the Ramadan prayer known as Tarawih and its’ ruling:
Imam Ahmad ibn Hanbal (d. 241 AH/AD 855), may Allah be pleased with him, says of Tarawih, “It is twenty raka`ah, but there is no harm in doing more than that.”
Imam Abul Qasim al-Khiraqi (d. 334 AH/AD 946), may Allah be pleased with him, was taught directly by the oldest son of the Imam, Salih ibn Ahmad, said, “The prayer in the month of Ramdan is to be 20 rak`ah.”
Imam Ibn `Aqil al-Baghdadi (d. 513 AH/AD 1120), may Allah be pleased with him, gave us this ruling, “Twenty raka`ah is the amount for Tarawih.” 
Imam Muwaffaq ud-Din Ibn Qudamah (d. 620 AH/AD 1223) reminds us, “And the sunnah is that Tarawih is prayed with the people a total of twenty rak`ah.” 
Imam Fakhr ud-Din Ibn Taymiyyah (d. 622 AH/AD 1225), may Allah have mercy on him, stated that it is to be twenty raka`ah.
Imam Baha’ ud-Din al-Maqdisi (d. 624 AH/AD 1227), may Allah be pleased with him, agreed with the position of his first cousin, Imam Muwaffaq ud-Din Ibn Qudamah and passed over the statement without comment.
Imam Majd ud-Din Ibn Taymiyyah (d. 653 AH/AD 1255), may Allah be pleased with him, an authority and one of the two highest voices in the Legal School of Imam Ahmad ibn Hanbal, stated, “The sunnah for Tarawih is twenty raka`ah.”
Imam Shams ud-Din Ibn Qudamah (d. 682 AH/AD 1283), may Allah be pleased with him, in his authoritative work, explains, “The number of raka`ah for Tarawih is twenty.” 
Imam Nur ud-Din `Abdur-Rahman ibn `Umar al-Basri ad-Darir (d. 684 AH/AD 1285), may Allah be pleased with him, gave the position from the early foundational source of the school that in Basrah in today’s Iraq: “Twenty rak`ah is the prayer for Tarawih and the sunnah.”
Imam Ahmad ibn Hamdan al-Harrani (d. 695 AH/AD 1296), may Allah be pleased with him, judge, expounder and master of fiqh, shared his wisdom, “The prayer of Tarawih is twenty rak`ah” 
Imam Ahmad ibn an-Najjar al-Futuhi (d. 695 AH/AD 1296), judge, jurist and theologian, re-iterates, “The sunnah for Tarawih is twenty raka`ah.” 
Imam Taqi ud-Din Ibn Taymiyyah (d. 728 AH/AD 1328), may Allah have mercy on him, although not an agreed upon voice, said the following, “As for Tarawih, if he prayed according to the madhhab of Abu Hanifah, Ash-Shafi`ii, Ahmad ibn Hanbal, which is twenty raka`ah; or if it was according to the madhhab of Malik, then it is 36 raka`ah; or if it is thirteen raka`ah, eleven raka`ah, then he has done well.” 
Imam Shams ud-Din Muhammad ibn Muflih (d. 763 AH/AD 1362) ruled correctly when he said, “Tarawih being 20 raka`ah is referred to as the best position.” 
Imam Muhammad ibn `Abdullah az-Zarkashi al-Masri (d. 774 AH/AD 1372), one of the great scholars of Egypt and one of the ‘great 400’ commentators on Imam al-Khiraqi’s al-Mukhtasar, had this to say, “Tarawih is a prayer of 20 raka`ah.” 
Imam Abu Bakr al-Jarra`ii al-Hanbali (d. 883 AH/AD 1478), the great Qadi and theologian, gives food for thought, “Tarawih is twenty raka`ah.”
Imam `Ala’ ud-Din `Ali ibn Sulaiman al-Mardawi (d. 885 AH/AD 1480), one of the great judges of times past, said, “Therefore, Tarawih is some twenty raka`ah.” 
Imam Musa ibn Ahmad al-Hajjawi (d. 968 AH/AD 1561), may Allah be pleased with him, gave the ruling, “Tarawih is twenty rak`ah in congregation and praying witr after that.” 
Imam Taqi ud-Din Muhammad ibn Ahmad al-Futuhi (d. 972 AH/AD 1564), may Allah be pleased with him, considered one of the greatest scholar of Egypt, Sudan, Northeast Africa, gives his understanding of righteous action in prayer, “So the prayer of Tarawih is 20 raka`ah.” 
Imam Mar`ii ibn Yusuf al-Karmi (d. 1033 AH/AD 1624), may Allah be pleased with him, gave his response on the subject, “Tarawih is composed of twenty raka`ah.” 
Imam Mansur ibn Yunus al-Buhuti (d. 1051 AH/AD 1641), may Allah be pleased with him, echoed what the ancients had given when he said, “And so Tarawih is twenty rak`ah.” 
Imam Salih ibn Hasan al-Buhuti (d. 1121 AH/AD 1709) gave the same ruling in his Maslak ur-Raghib Sharhu Dalil it-Talib.
Imam `Abdul Qadir ibn `Umar at-Taghlabi (d. 1135 AH/AD 1723) gave his ruling, “The number of Tarawih is twenty raka`ah.” 
Imam Muhammad ibn Ahmad as-Saffarini (d. 1188 AH/AD 1774), may Allah be pleased with him, gave the same position of the others in his text, Sharh ud-Dalil it-Talib, Book of Prayer under the chapter of Optional Prayers.
Imam Mustafa ad-Dumi al-Hanbali (d. 1200 AH/AD 1786) gave an identical ruling in his text.
Imam `Abdul Ghani al-Lubadi an-Nabulsi (d. 1319 AH/AD 1901) advised us in the prayer, “Tarawih is a prayer of twenty raka`ah.” 
Imam Ibrahim ibn Muhammad Duwayyan (d. 1353 AH/AD 1934), may Allah have mercy on him, when listing sunnah actions of the prayer, remarked, “And the prayer of Tarawih is twenty raka`ah in total.”
Imam `Abdullah ibn Muhammad al-Khalifi (d. 1416 AH/AD 1995), may Allah have mercy on him, made this statement, “Tarawih is 20 raka`ah, performed after the night prayer in the month of Ramadan.” 
 An-Nukat wal-Fawa’id us-Sanniyyah `ala Mushkil il-Muharrar, vol.1, pp. 89-90
 Mukhtasar ul-Khiraqi, pp. 29-30.
 At-Tadhkirah fil Fiqhi `ala Madhhab il-Imam Ahmad ibn Muhammad ibn Hanbal, Book of Prayer, under the chapter of the Description of the Prayer.
 This and his additional statements are from Al-`Umdah, pp. 24-25; Al-Kafi fi fiqh il-Imam Ahmad ibn Hanbal, vol. 1, pp. 180-181; Al-Mughni, vol. 1, pp. 833-834.
 Ghayat ul-Matlab fi Ma`rifat il-Madhhab, pp. 52-54.
 Al-`Uddah, Sharh ul-`Umdah, pp. 111-113
 Al-Muharrar fil-Fiqh `ala madhhab il-Imam Ahmad ibn Hanbal, vol.1, pp. 89-90.
 Ash-Sharh ul-Kabir, vol.1, pp. 783-784.
 Al-Wadihu fi Sharhi Mukhtasar il-Khiraqi, vol.1, pp. 216-218.
 Ar-Ri`ayat us-Sughrah, vol.1, pp. 85-86.
 Ma`unatu Uwl in-Nuha bi-Sharh il-Muntaha, vol.1, pp. 104-105.
 Al-Ikhtiyarat ul-Fiqhiyyah, pp. 63-64.
 An-Nukat wal-Fawa’id us-Sanniyyah `ala Mushkil il-Muharrar, vol.1, pp. 89-90.
 Sharh uz-Zarkashi `ala Mukhtasar il-Khiraqi, vol.1, pp. 542-543.
 Ghayat ul-Matlab fi Ma`rifat il-Madhhab, pp. 53-54
 Al-Insaf fi Ma`rifat ir-Rajihi min al-Khilafi `ala Madhhab il-Imam Ahmad ibn Hanbal, vol.1, pp. 430-440.
 Zad ul-Mustaqni` fi Ikhtisar il-Muqni`, pp. 50-51.
 Daqa’iq Uwl in-Nuha Li-Sharh il-Muntaha, vol.1, pp. 377-378.
 Manar us-Sabil fi Sharh id-Dalil, vol 1, pp. 87-88.
 Ar-Rawd ul-Murbi` bi-Sharhi Zad il-Mustaqni`, pp. 100-101.
 Nail ul-Ma’aarib bi-Sharhi Dalil it-Talib, vol.1, pp. 142-143
 Hashiyah `ala Nail il-Ma’arib, pp. 366-367
 Hashiyat ul-Labadi `ala Nail il-Ma’aarib fil-Fiqh il-Hanbali, pp. 70-73.
 Manar us-Sabil fi Sharh id-Dalil, vol.1, pp. 87-89.
 Kitab Irshad il-Mustarshid il-al-Muqaddam fi Madhhabi Ahmad, pp. 68-69.