The reality of al-mudraj: the mixing of what belongs to one speaker with what belongs to another, without any indication of where one ends and the other begins.1
Al-mudraj is of two categories: the first, mudraj al-matn (insertion within the matn); the second, mudraj al-sanad (insertion within the chain).
Mudraj al-matn may occur at the beginning of the matn, in its middle, or at its end, the last being the most common.2
Mudraj al-isnād takes a number of different forms.
Idrāj is detected by a more detailed narration that distinguishes the inserted portion from the rest of the ḥadīth, by an explicit statement from the narrator himself, or by an explicit statement from one of the well-informed imāms.3
Al-Sakhāwī said this in Sharḥ al-Taqrīb, p. 160. ↩
An example: what al-Bukhārī narrated (1/25, no. 136) from Abū Hurayra, who said: "I heard the Messenger of Allāh ﷺ say: 'On the Day of Resurrection my community will be summoned, with shining faces and limbs from the marks of wuḍūʾ; so let whoever among you can lengthen the radiance of his face do so.'" The statement "So let whoever among you…" is mudraj from the words of Abū Hurayra himself, as al-Ḥāfiẓ and others have pointed out. And Allāh knows best. ↩
Sharḥ Nukhbat al-Fikr, pp. 61–63; and others. ↩
A muʿallal ḥadīth contains a hidden defect (ʿilla) damaging to its soundness, detected by warning signs in sanad and matn that arise to one familiar with the art.
Al-gharīb falls into two categories: al-fard al-muṭlaq (absolute solitary) and al-fard al-nisbī (relative solitary).
A ḥadīth narrated through different but closely comparable routes that cannot be reconciled is al-muḍṭarib; iḍṭirāb renders it weak, as it implies an absence of ḍabṭ.
A ḥadīth in which a narrator has been replaced with another, whether one narrator, several, or even the entire chain, is al-maqlūb (literally, that which has been inverted).
