In Islam, we have
isnad i.e. the chain of reporters which enables the sayings or actions of either the Prophet Muhammad (pbuh) or any of his companions to be accurately and reliably traced in every part of the narration all the way up to the original source of the narration.
Islam is the ONLY religion which has
isnad and there is a Science of Hadith which classifies all of the countless thousands of collected ahahith into categories depending on the strength and quality of each hadith – sound, reliable, weak or fabricated.
A hadith (pl. ahadith) is composed of two parts: the
matn (text) and the
isnad (chain of reporters). A text may seem to be logical and reasonable but it needs an authentic isnad with reliable reporters to be acceptable; 'Abdullah bin Al-Mubarak (d. 181 AH), one of the illustrious teachers of Imam al-Bukhari, said,
"The isnad is part of the religion: had it not been for the isnad, whoever wished to would have said whatever he liked"
Suppose that someone claims that one of the apostles said so and so about something that Jesus (pbuh) might have said and did, can any Christian scholar then provide a chain of narration which traces precisely how this narration was transmitted from the person who finally wrote it down all the way up to the person who heard either what the said apostle said or what Jesus (pbuh) himself said?
In Islam, Muslim scholars can indeed provide this precise chain of narration regarding not only what exactly did the Prophet Muhammad (pbuh) say but also the name and personal character of every person along this chain of narration who reported this narration until it was compiled in a book of Hadiths.
This is what is termed
isnad and you can learn a bit more on ‘
isnad’ and the ‘
Science of Hadith’ at Wikipedia.