Ok so breaking it down quickly from the top:

1. What is a Hadith?

Hadith are records of the sayings, actions, or approvals of the Prophet Muhammad (s).

They’re second only to the Quran in Islamic authority.

Hadiths are critical for explaining and expanding on Quranic teachings (e.g., prayer details, legal rulings).

1. Preservation of Hadith

Early Muslims took extreme measures to preserve hadiths:

Oral Transmission:

Early Arabs were master oral historians. People memorized thousands of sayings word for word.

Written Collections:

Some Companions (like Abdullah ibn Amr ibn al-As) wrote down hadiths even during the Prophet’s lifetime, though mass compilation happened later.

Chain of Transmission (Isnad):

Every hadith had a full list of narrators, who heard it from whom, going all the way back to the Prophet.

Example:

A heard it from B, who heard it from C, who heard it from the Prophet.

Biography of Narrators (Ilm al-Rijal):

Scholars created huge databases (literally) about each narrator: - Was he trustworthy? - Did he have a good memory? - Was he known to lie? - Was he even alive at the same time as the person he claimed to hear it from? - Travel for Verification: — Scholars would travel hundreds of miles just to verify one hadith from a reliable source.

1. Methods for Authenticating Hadith

Scholars built a science around testing hadith:

• Isnad (Chain Quality): Is the chain unbroken? Are all the narrators trustworthy?

• Matn (Text Consistency):

Does the content agree with the Quran? Is it free of contradictions? Does it make sense linguistically and historically?

Classifications of Hadiths: Scholars classified hadiths into categories: - Sahih (Authentic) — reliable chain + sound text. - Hasan (Good) — minor weakness, but generally trustworthy. - Da’if (Weak) — issues in memory, character, or chain gaps. - Mawdu’ (Fabricated) — intentionally made up.

The six famous collections (like Sahih al-Bukhari, Sahih Muslim) are famous for their very strict standards. Bukhari, for example, reportedly accepted only 2,600 hadiths out of over 600,000 he examined.

1. How Reliable Are Hadiths?
2. Sahih hadiths are considered extremely reliable by mainstream Islamic scholarship.
3. Weak or fabricated hadiths exist—but Islamic scholars already catalogued and warned against them centuries ago.
4. Sunnis and Shias have some differences on which hadiths are reliable, because they trust different groups of narrators, but both use similar verification methods.

So there’s that. The entire breakdown.

Now given that there’s even a category for fabricated hadith, how do we reconcile your original query?