There is no sound report to indicate that in Ramadan the Prophet (blessings and peace of Allah be upon him) prayed twenty rak‘ahs, even though that is permissible
Praise be to Allah
This hadith was narrated from Ibn ‘Abbaas (may Allah be pleased with him, that the Messenger of Allah (blessings and peace of Allah be upon him) used to pray twenty rak‘ahs and Witr in Ramadan.
This was narrated by Ibn Abi Shaybah in al-Musannaf (2/164); ‘Abd ibn Humayd – as it says in al-Muntakhab (no. 653); at-Tabaraani in al-Mu‘jam al-Kabeer (11/393) and al-Mu‘jam al-Awsat (1/243); al-Bayhaqi in as-Sunan al-Kubra (2/69 8).
All of them narrated it via Abu Shaybah Ibraaheem ibn ‘Uthmaan, from al-Hakam ibn ‘Utaybah, from Muqsim, from Ibn ‘Abbaas.
No one narrated this hadith from al-Hakam except Abu Shaybah, and it was not narrated from Ibn ‘Abbaas except via this isnaad.
This Abu Shaybah Ibraaheem ibn ‘Uthmaan is al-Kufi al-‘Absi. The scholars of hadith are unanimously agreed that his hadith is weak and is to be rejected. In fact Ibn al-Mubaarak said concerning him: Cast his hadith aside. Ahmad ibn Hanbal classed him as very weak (da‘eef jiddan) and also said concerning him: His hadith munkar (odd) and weird, and he is close to al-Hasan ibn ‘Amaarah, and the hadith of al-Hasan ibn ‘Amaarah is to be rejected. An-Nasaa’i said: His hadith is to be rejected. Abu Haatim said: They rejected his hadith. See his biography in Tahdheeb at-Tahdheeb (1/145).
Therefore the scholars classed this hadith as weak. Ibn Battaal said: This Ibraaheem is the grandfather of Banu Shaybah, and is da‘eef. His hadith does not constitute evidence. What is well-known is that praying qiyaam with twenty rak‘ahs in Ramadan is something that was narrated from ‘Umar and ‘Ali.
End quote from Sharh Saheeh al-Bukhaari (3/141)
Az-Zayla‘i (may Allah have mercy on him) said:
The hadith is problematic because of Abu Shaybah Ibraaheem ibn ‘Uthmaan, the grandfather of Imam Abu Bakr ibn Abi Shaybah, and there is consensus that he is da‘eef. … Moreover, it is contrary to the saheeh hadith from ‘Aa’ishah: He [the Prophet (blessings and peace of Allah be upon him)] did not pray more than eleven rak‘ahs [in qiyaam] in Ramadan or otherwise.
End quote from Nasab ar-Raayah (2/153).
It was also classed as da‘eef by all of the following: Ibn ‘Abd al-Barr in at-Tamheed (8/115); al-Bayhaqi in as-Sunan al-Kubra (2/698); Ibn Mulqin in al-Badr al-Muneer (4/350); al-Haythami in Majma‘ az-Zawaa’id (3/173); Ibn Hajar al-Asqallaani in ad-Diraayah (1/203). In Mizaan al-I‘tidaal, adh-Dhahabi regarded it as munkar (odd). Ibn Hajar al-Haytami said in al-Fataawa al-Kubra (1/195): It is extremely da‘eef. It was classed as da‘eef by al-Qastallaani in al-Mawaahib al-Laduniyyah (3/306) and by as-Suyooti, as it says in al-Haawi (1/413). Al-Albaani deemed it to be fabricated (mawdoo‘), as it says in as-Silsilah ad-Da‘eefah (560).
Thus it is clear that the scholars are unanimously agreed that this hadith is to be classed as weak.
It is proven in Saheeh al-Bukhaari and elsewhere that ‘Aa’ishah (may Allah be pleased with her) was asked about the night prayer (qiyaam) of the Messenger of Allah (blessings and peace of Allah be upon him) during Ramadan, and she said: he did not do more than eleven rak‘ahs in Ramadan or otherwise.
Here is ‘Aa’ishah (may Allah be pleased with her), telling of the actions of the Messenger (blessings and peace of Allah be upon him). If the Messenger (blessings and peace of Allah be upon him) had prayed Taraweeh with twenty rak‘ahs, that would not have been unknown to ‘Aa’ishah (may Allah be pleased with her)
With regard to the number of rak‘ahs of Taraweeh prayer, we have discussed that previously in the answers to questions no. 82152 and 9036.
With regard to some people describing their opponents as Wahhabis, please see fatwas no. 10867 and 120090
And Allah knows best.