This is the summary of Shaykh Mahmud al-Zayn's discussion again. The best thing about the discussion is that he does justice to both sides and presents both methodologies, not generalizing based on what he opines:
Shaykh Dr Mahmud Ahmad al-Zayn discusses the evidence in favour of group dhikr here and in doing so he explains the different understandings of bid'ah, confirming the divergence I described above.
The dominant approach was that of Imam al-Shafii, who believed general principles may be applied specifically as they are included under those general principles. So, for example, in Kitab al-Dhabaih of al-Umm, he recommends reading salawat on the Prophet (sallallahu alayhi wa sallam) after saying bismillah allahu akbar while slaughtering the animal - and he deduces this from the general command in Surat al-Ahzab (33:43) of sending salawat on the Prophet (sallallahu alayhi wa sallam).
This is contrasted with Imam Malik's answer to this question that no salawat can be read after saying bismillah allahu akbar, nor can one do so upon saying alhamdulillah (or alhamdulillah 'ala kulli hal) after sneezing. (also mentioned in al-Umm). In this latter view, in order to for there to be persistence (iltizam) on a particularised form (taqyid) of a general command (itlaq), there must be specific evidence. Al-Shatibi calls this takhsis al-umum bi la dalil (specifying a general principle without evidence), which in his view is impermissible but in the first view expounded above is permissible.
The general command to do good (22:77) can, according to the first view, be used to institutionalise or invent specific modes of devotional acts, so long as they do not oppose the legal requirements of the Shariah. However, this approach itself does not necessarily yield the same result because of the variable of "not contradicting the Shariah". Al-Zayn gives the example of Salat al-Raghaib and the dispute between two Shafiis: Ibn al-Salah and al-Izz ibn Abd al-Salam - both of them ascribe to the aforementioned Shafii methodology. Ibn al-Salah considers the Salah with its particular features (awsaf khassah) permissible and desirable as it falls under the general desirability of "Salah". Al-Izz Ibn Abd al-Salam agrees on the principle: according to him bid'ah is any new act after the Prophet's lifetime and they are simply regulated according to the normal ethical categories of mubah, hasan or sayyi'ah (permissible, good or bad); mubah is that which the Shariah is silent upon like different types of food, hasan is that which agrees with legal requirements within broad principles and sayyiah is that which opposes legal requirements. On the question of Salat al-Raghaib al-Izz ibn Abd al-Salam considers it a bad bid'ah because it contradicts the Shariah by having unique properties that the Shariah has disallowed. Hence, both Ibn al-Salah and al-Izz agree with the Shafii principle, but disagree over the outcome on this particular question because of their different understandings of a legal ruling.
Importantly, al-Zayn reminds us, the terms "hasan" and "sayyi'ah" have been used differently. Al-Izz ibn Abd al-Salam believes all acts after the Prophet's lifetime legally (shar'i) bid'ah and not just linguistically (lughwi), whereas others equated legal bid'ah to bad bid'ah and linguistic bid'ah to all five categories. This is a semantic difference within this methodology itself.
This methodology is "open" as it can accommodate a very many different manifestations of worship within the foundations and principles of Shariah. The second methodology ascribed to Imam Malik above is "closed" as it restricts itself to particular past precedents. It could be said the first is "forward-looking", hence creative, and the second "backward-looking", hence puritanical. A major exponent of this latter approach is al-Shatibi who said unless a particular mode of devotion is done spontaneously or due to free-time (faragh) or depending on one's physical strength (nashat), that particular form would require evidence. He, for example, opposes du'a after Salah on the basis that it is attached significance in that particular time; however since in the act of making du'a one must specify time, place etc., if it is done without persistence (iltizam) and with the reason of convenience, it will be permissible. In other words, it is the institutional specification of an unprecedented act that al-Shatibi would oppose.
Both of the above approaches, of al-Shafii and of Malik, have evidence from the practice of the Sahabah. In favour of al-Shafii's approach are the following incidents:
1. According to Anas, an Imam from the Ansar would recite Surat al-Ikhlas in every first rakat, and when asked by the Prophet (sallallahu alayhi wa sallam) why he replied because he likes the surah, and the Prophet (sallallahu alayhi wa sallam) approved of this (al-Bukhari) - the man specified through persistence (iltizam) the recitation of a particular sura through his own judgement and preference and this was condoned by the Prophet (sallallahu alayhi wa sallam)
2. Abu Hurayra narrates that Khubayb ibn Adi was the first to initiate the practice (sunna) of reading two rak'ats before being executed (Bukhari) - here again a general recommendation of Salah is specified in time (waqt) and situation (hal)
3. Abu Said al-Khudri narrated the story when he and some Companions treated a village leader using Surat al-Fatiha and the Prophet (sallallahu alayhi wa sallam) later asked them "how is it that you knew it is a cure (ruqya)?" (Bukhari) - in other words, they took the general notion of the Qur’an being a cure (shifa) and applied it in a specific way
The view of Malik is supported by some of the actions of the Sahabah:
1. Ibn Umar opposed Salat al-Duha and Du'a Qunut declaring the "bid'ah" even though they may be included under general principles
2. Abd Allah ibn Mas'ud opposed group dhikr as bid'ah even though it may be included in the general practice of dhikr (Darimi)
3. Ibn Umar also opposed a man who said "alhamdulilla wa salamun ala rasulillah" upon sneezing saying "I also accept alhamdulillah and salamun ala rasulillah but this is not the way the Prophet (sallallahu alayhi wa sallam) taught us; he taught us to say 'alhamdulillah ala kulli hal'" (Tirmidhi)
These are just some examples of how each of these two methodologies function. As would be expected, the Shafii madhhab adopts the first methodology and according to Ibn Daqiq al-Id "the Malikis have tended towards this second (approach)" (wa mayl al-malikiyya ila hadhi l-thaniyah), but al-Zayn says this does not mean all Malikis took this view so we find for example Ibn 'Arafa saying about du'a after Salah "if it is done with the intention that it is from the sunnas of Salah it is impermissible but if it is free from this, then it remains according to the general ruling of du'a which is that it is a prescribed worship whose virtue and greatness is recognised in the Sharia". There were many Malikis, however, that followed Malik and al-Shatibi and did not allow the specification of general principles, and their rejection of mawlid derives from this (as with ibn al-Hajj, al-Haffar and many others as mentioned above).