Is the introduction to Sahih Muslim a part of it, or separate from it? Did the author write it as a part of it or as a separate entity? What is its subject matter? And is it known as "The Introduction"?

The "Introduction to Sahih Muslim" comprises a few pages written by Imam Muslim before the hadiths of "As-Sahih." Imam Muslim did not name it himself, but it came to be called "The Introduction" or "The Book's Preface." It addressed the reason for the book's composition, its subject matter, its methodology, and some issues related to the science of hadith. The introduction is considered part of the book in terms of narration and transmission, but it is not part of "As-Sahih" in terms of subject matter and content, as Imam Muslim began the hadiths of the book thereafter. Scholars distinguish between "The Introduction" and "As-Sahih"; thus, they do not say, "Reported by Muslim in his Sahih" for what is mentioned in the introduction, and they differentiate between the narrators of the introduction and the narrators of "As-Sahih."