«الْمُدْرَجُ»
Mudraj is transmitted material into which another element has been incorporated so that it appears to belong to the original transmission.
The essential failure is loss of the boundary between sources. Different chains may be conflated into one chain; or words of a Companion, Successor, or later narrator may be merged into the prophetic wording. Insertion does not automatically establish deliberate forgery: a mistake, abbreviation, or the flow of speech may be responsible.
Illustration: A teacher reads a hadith and then explains what it means. If a student transmits the explanation without identifying it, the matn may acquire an interpolation. Critical study must separate the original wording from the explanatory addition.