By whom? You're confusing the hadiths with the Nicean Council. Its the fake Gaspels that are quoted and revered, not the Hadiths.
Hadith are generally categorized as sahīh (sound, authentic), da`īf (weak), or mawdū` (fabricated). Other classifications used also include: hasan (good), which refers to an otherwise sahīh report suffering from minor deficiency, or a weak report strengthened due to numerous other corroborating reports; and munkar (ignored) which is a report that is rejected due to the presence of a solitary and generally unreliable transmitter.[8] Both sahīh and hasan reports are considered acceptable for usage in Islamic legal discourse. Classifications of hadith may also be based upon the scale of transmission. Reports that pass through many reliable transmitters at each point in the isnad up until their collection and transcription are known as mutawātir. These reports are considered the most authoritative as they pass through so many different routes that collusion between all of the transmitters becomes an impossibility. Reports not meeting this standard are known as ahad, and are of several different types.[3]
Another area of focus in the study of hadith is biographical analysis (`ilm al-rijāl, lit. "science of people"), in which details about the transmitter are scrutinized. This includes analyzing their date and place of birth; familial connections; teachers and students; religiosity; moral behaviour; literary output; their travels; as well as their date of death. Based upon these criteria, the reliability (thiqāt) of the transmitter is assessed. Also determined is whether the individual was actually able to transmit the report, which is deduced from their contemporaneity and geographical proximity with the other transmitters in the chain.[9] Examples of biographical dictionaries include Ibn Hajar al-Asqalani's "Tahdhīb al-Tahdhīb" or al-Dhahabi's "Tadhkirat al-huffāz."[10]
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