Al-Izz ibn Abd al-Salam, called Sultan al-Ulama, systematized the five-category analysis of bid'a (obligatory, recommended, neutral, disliked, forbidden) that Imam al-Nawawi and others applied in their commentaries.
This framework shows that bid'a in Sacred Law is not a single blanket ruling but depends on how an act relates to revelation.
The concept of bid'a
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Primary lecture and articles on innovation in Sharia.