Imam al-Nawawi died young yet authored works that define Sunni curriculum to this day: his commentary on Sahih Muslim, al-Adhkar (authorized remembrance), Riyad al-Salihin, and al-Minhaj in Shafi'i fiqh.
He explains how general hadith texts are qualified by legal theory — for example, the classification of bid'a into five moral categories in his Sharh Muslim. His books are standard in mosques and schools globally.
The concept of bid'a
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Lecture and resources aligned with classical definitions.