All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
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.
So, nobody can ask which Sunnah we are to follow, the Prophet's Sunnah or ‘Umar's. ‘Umar did not do any form of worship that had any contradiction to the Prophet . ‘Umar never contradicted the Prophet or the Prophet’s Sunnah. ‘Umar ranked high regarding the Religion of Allaah and adherence to the Sunnah. Nobody can deny such a matter. The Prophet gave witness many times that ‘Umar is to be in Paradise. Many times his opinion coincided with the revelation. He was a defender of the Sunnah and fighter against innovation; .
Also, the Companions sanctioned ‘Umar's deed, and there was a consensus on it, and such a deed became the Sunnah of the rightly guided Caliphs ‘Uthman and 'Ali .
Here, it is useful to state that Abu Bakr did not do such a deed, even though he knew that there is no legislation that would be made obligatory after the death of the Prophet for the following two probabilities that Al-Baaji stated:
Firstly (1), Abu Bakr, was busy fighting the apostates and the period of his rule was very short, and secondly (2) he thought it was better to let people perform the night prayers in the third part of the night rather than performing the Taraweeh in the first part of the night.
As regards the number of Rak'ahs of the Taraweeh prayer, then there is no specific number confirmed from the Prophet in this regard. Ibn Taymiyah said: “If a person believes that the Prophet had specified a specific number of Rak’ahs in night prayers in Ramadan, and he is not allowed to add to it or decrease from it [number], then he is wrong.”
Besides, As-Suyooti said: “It is proved in the Sunnah that one is advised to pray the Taraweeh prayer without fixing a number to it, and it was not confirmed that the Prophet performed 20 Rak'ahs as Taraweeh, but he prayed it for some nights and the number of Rak'ahs was not mentioned.”
Therefore, we only have the practice of the Companions and it was confirmed that they used to perform 20 Rak'ahs, and this is the opinion of the Shaafi'i, Hanafi, Hanbali and the opinion of the majority of scholars, and it is one opinion of the Maaliki School as well, which was considered as the preponderant opinion by some scholars of their school. Ad-Dasooqi said: “It was the practice of the Companions and their followers.” Moreover, Ibn ‘Abideen said: “This is the practice of the people east and west.”
An-Nawawi said: “In our view (according to our School) it (i.e. Taraweeh) is 20 Rak'ahs with a Tasleem after each two Rak'ahs. This is apart from the Witr prayer. Abu Hanifa and his followers, Ahmad, Dawood and others hold the same opinion.” Besides, Al-Qadi Iyad reported this from the majority of the scholars.
Ibn Qudamah after mentioning evidence that it is 20 Rak’ahs, he said: “This is almost a consensus.”
So for most scholars performing twenty Rak'ahs Taraweeh is the best. But according to Ibn Taymiyah this depends on the state of the worshipers. Ibn Taymiyah said: “The preference depends on the worshippers. If they can bear standing for a long time in prayer, then they can perform 10 (long) Rak'ahs and 3 Witr as was the practice of the Prophet in Ramadan and at other times, and that is best for them. But if they can't bear standing for a long time in prayer, then they can perform twenty Rak'ahs (i.e. short ones) and that is best for them; this number is the common practice among the Muslims and this is an average between 10 and 40. If they can perform forty Rak'ahs or any other number, then this is permissible and nothing is disliked in this respect. This is the opinion of many of our Imaams such as Ahmad and others.”
As regards your question concerning whether or not the Prophet divided innovation (Bid'ah) into good and bad, then the answer is "No". Rather, it is confirmed that the Prophet said: ''Every innovation is misguidance." [Muslim] The scholars agreed that this Hadeeth is authentic and they agreed on providing it as evidence but they differed about whether this Hadeeth indicates a general rule about every innovation or that it is limited in scope and its application can be modified by other Ahadeeth.
The scholars are of two opinions:
1- Some believe it is limited and the meaning of the Hadeeth is that every innovation that contradicts the Quran, the Sunnah and the consensus of the scholars is a misguidance. Imam An-Nawawi said: “The scholars stated that innovation is of five kinds: obligatory, recommended, forbidden, disliked and permissible.” He added: “The Prophet's words "every innovation" does not exclude that this Hadeeth is general but specified by other evidence as "every", here is for emphasis as Allaah says: (everything) in the verse {Destroying everything by the Command of its Lord! …….} [Quran 46:25]”
Ibn Hajar said: “Originally innovation means something without previous example (case). In the Sharee'ah, it is what contradicts (or opposes) the Sunnah, so it is dispraised. So, if it comes under what is good and praiseworthy in the Sharee'ah, then it is good, and if it comes under what is disgraceful then it is rejected, otherwise it is classified under what is permissible and it may be divided into the 5 previous kinds.”
Ibn Hajar added: “Al-Bayhaqi reported from Ash-Shaafi'i that: “Innovation is of two kinds: (1) if it contradicts the Quran, the Sunnah or the consensus of the scholars, then it is an innovation of misguidance, and (2) if it does not contradict the Quran, the Sunnah, or the consensus of the scholars, then it is not dispraised. Some scholars divided innovation into five kinds as mentioned above and this is clear.” [End of quote]
Al Qarafi said: “The correct opinion is the one that divides innovation into five kinds.”
To conclude, those who chose the above opinion is Ash-Shaafi'i, Al-Khattaabi, Al-Qarrafi, An-Nawawi, Ibn Hajar, Ibn ‘Asaakir, Abu Shaama, Al-Iz Ibn ‘Abdus-Salaam, As-Suyuti, Az-Zarkashi, Ibn Jizzi, As-Sakhawi, Ad-Dassooqi and Al-Khaadimi.
2- The second opinion considers the Hadeeth to be general, i.e. every innovation is misguidance. Most scholars of the Maaliki School, Ibn Taymiyyah and Imaam Al-Shaatibi reject innovation to be divided into five kinds.
Shaykh Ibn Taymiyyah said: “Any innovation that is not obligatory or recommendable is a bad innovation and a misguidance according to the agreement of all the Muslims. The scholars who said that some of the innovations may be good, then this applies if there is Islamic evidence that proves its desirability. No Muslim would say that what is not desirable or obligatory is among the good deeds by which one gets closer to Allaah. So, whoever gets closer to Allaah by doing something that is not among the good deeds that are ordained, and not only desirable, then he is misguided and following the devil and his way.”
Shaykh Ibn Taymiyyah also said: “It is known that every deed that was not practiced or recommended by Allaah's Messenger or done by those who are followed as examples for Muslims in their religion, then it constitutes a rejected innovation and no one would say about such a matter that it is a good innovation. Therefore, a good innovation according to the scholars who classified innovation to good and bad, is that it should be classified as desirable by some scholars who are followed as examples and that there is Islamic evidence that it is desirable. Similarly, those who believe that every innovation in Sharee'ah is an innovation, hence dispraised, rely on the Hadeeth which reads: “Every innovation is misguidance.”
As for the saying of ‘Umar on Taraweeh prayer: “How good an innovation it is!” He meant innovation considering the general linguistic meaning. But, the innovation in the Sharee'ah is every deed that has no evidence in the Sharee'ah. So, both opinions have the same meaning.
In other words, the scholars agreed that what is not desirable or obligatory in the Sharee'ah is not considered as desirable or obligatory. So, whoever performs a deed as a form of worship which is not obligatory or desirable in the Sharee'ah, is misguided according to the agreement of all the Muslims.
He also added: “I explained in more than one book that it is a Muslim's duty to adhere to the general meaning of the Prophet's Hadeeth: "Every innovation is a misguidance.”; and that it is an obligation to act according to its general meaning.”
Those who divide innovation to good and bad and take this as an excuse to not reject an innovation or consider it as forbidden [or disliked], then they are wrong, like the Sufi sect and other misguided sects as they claim that no innovation is disliked except that which contradicts the Sharee'ah. Anything that is called innovation and proved to be good is in one of two things: Either we say this is not an innovation in religion even if it is linguistically called innovations such as ‘Umar's saying about Taraweeh. Or that it is a generalization with some specific exception that contradicts the general rule for some dominant evidence like all generalizations in the Quran and the Sunnah as I clearly stated in my two books: Qaa’idatus-Sunnah wal Bid'ah' and Iqtidhaa’ As-Siraat Al-Mustaqeem (Following the Straight Path).”
In conclusion, there is a big difference of opinion concerning dividing innovation into kinds and categories and many books were written in this regard. Those who divide innovation into categories, their opinion is accepted by those who oppose them, but they classify it under what is known in the Sharee'ah as Al-Maslahah Al-Mursalah: public interest, (meaning that there is no text (Quran and Hadeeth) for considering it as desirable or forbidden.), and they do not call it innovation.
Allaah Knows best.