When evaluating the credibility of a hadith, many factors are taken into account:
Regarding the completeness of the chain, a hadith is
a. musnad (مسند) – if it can be referred to the Prophet (s) without gaps in the chain.
b. muttaṣil (متصل) – if it can be referred to its source (other than the Prophet (s)) without any gaps in the chain.
c. munqaṭi’ (منقطع) – if there is a gap somewhere in the chain (it can be be anywhere in the chain, and it may a single link or serveral links that are missing). More specifically, a hadith is called
d. mu’ḍal (معضل) – if two or more consecutive links are missing in the chain
mursal (مرسل) – if it is narrated by a Tabi’i directly from Prophet (Salla Allah’aleihi wasallam) without the Sahabi being mentioned.
e. mudallas (مدلس) – if the last narrator omits or tries to hide the name of his Sheikh
maqlūb (مقلوب) – (a) if the two names misplaced in the chain, or (b) if the entire chain replaced with another chain
2. The individual narrators. A person is called:
ḍābiṭ (ضابط) – if he is precise and has a good memory
a. ‘adl (عدل) – if he is righteous
b. majhūl (مجهول) – if it is not known if he existed, or if his character is unknown
It also taken into account when and where the narrators lived. E.g. if two successive narrators lived at the same time, it is reasonable that they met each other, unless it is known that they never met.
Furthermore, the circumstaces under which the hadith is narrated are considered. E.g. a person who in his youth is considered to be thiqa (reliable), may have become forgetful at old age. He is then no longer considered to be thiqa.
A hadith is called
C. mubham (مبهم) – if any person in the chain, or any person mentioned in the hadith, is not mentioned clearly by name.
3. The content of the matn. A hadith is called
shādhdh – when it contradicts one another hadith that is more credible.
The more credible hadith is then called maḥfūzh (محفوظ).
a. munkar (منكر) – a weak hadith is rejected because it goes against a more credible hadith. The opposite is Ma’ruf (معروف).
b. mudraj (مدرج) – if any of the words of the re-narrator is accidentally incorporated in hadith
Overall assessment. A hadith called
a. mu’allal (معلل) – if the hadith has some subtle weakness, which only hadith scholars with great insight are able to detect
b. muḍṭarib (مضطرب) – if different hadith scholars have variying but equally strong opinions about the status of chain or the content content of the hadith.
c. matrūk (متروك) – a weak hadith, which is narrated by a single unreliable person, and whcih is rejected unanimously by hadith scholars.