«وَالْمَتْنُ: هُوَ غَايَةُ مَا يَنْتَهِي إِلَيْهِ الْإِسْنَادُ مِنَ الْكَلَامِ»
The matn is the wording at which the chain ends.
The chain carries a report to its actual narrated content. A matn need not be a directly quoted Prophetic statement; a report attributed to a Companion or Successor likewise has a chain and a narrated content.
Application: In “From Ibn ʿUmar, who said: …,” the transmitters leading to Ibn ʿUmar belong to the chain, and the subsequent statement is the matn. Whether it is categorized as marfūʿ or mawqūf is a different classification, determined after recognizing the elements of the report.