[Interpolated Matn]
As for (1) interpolated matn, it occurs when words are inserted into the matn that do not belong to it. At times the insertion is found at the beginning, at times (2) in the middle, and at times at the end—the most common case—because it usually happens by linking (3) one sentence to another, or by merging (4) a mawqūf statement—words of a Companion or someone after them—with a marfūʿ statement—words of the Prophet ﷺ—without any break. Such is interpolated matn.
[How is interpolation detected?]
Interpolation is recognized when a (5) narration appears that clearly distinguishes (6) the interpolated portion from that (7) into which it was inserted (8); or when the narrator, or one of the well-informed imams, explicitly states this; or when it is impossible that the Prophet ﷺ could have uttered those words.
Al-Khaṭīb authored a dedicated work (9) on the subject. I have abridged it and added to it about twice as much—or even more (10)—and all praise is due to Allah.
[The Inverted Report]
(Or) if the discrepancy results from reversing the order (11), that is, (12) in