Over the course of reviewing aḥādīth, one may come across these two terms related to aḥādīth; the isnād and the matn of a ḥadīth. These are the two basic parts of which a ḥadīth consists of. The meaning of these two terms will be explained below, ʾIn shāʾ Allāh:
The isnād is the chain of narrators which connects to the matn of a ḥadīth, that is, the narrators who conveyed and transmitted the matn, beginning with the last narrator, who is the author of the book of ḥadīth, and ending with the Prophet (ﷺ).
The matn is the wording of a ḥadīth, which conveys the meaning. The scholars refused to accept any aḥādīth which does not have an isnād due to the spread of lies against the Prophet (ﷺ).
Muḥammad ibn Sirīn (رحمه الله) said regarding this issue:
"They (i.e, the scholars) did not use to ask about the isnād, then when the fitnah occured, they would say: 'Name for us your rijāl (men, i.e, narrators)', then they would see who were the people of the Sunnah and accept their ḥadīth and they would see who were the people of bid'ah (innovation) and reject their ḥadīth." (1)
Bārik Allāhu Fīkum. May Allāh bless you, and shukran.
Sources :
All information regarding the isnād and the matn was taken from the book, Following the Sunnah of the Prophet (ﷺ), with minor changes to the original wording.
1. Foreword of Ṣaḥīḥ Muslim (1/84 and 87), from al-Nawawī's explanation of it.