ما هو الحديث المعلّل وما حكمه؟

"Al-Hadith al-Mu‘allal" (the defective hadith) is a hadith that contains a hidden defect (illah) which impairs its authenticity, even though outwardly it appears sound. Examples include a break in the chain of narration (sanad), replacing a trustworthy narrator with a weak one, subtle deception (tadlees khafi), an interpolation in the text (matn), or an anomalous addition.