Besides the reasons mentioned by al-Nawawi for fabricating...
Besides the reasons mentioned by al-Nawawi for fabricating the hadith and falsifying the Messenger’s traditions, many others are there that were stated by the ulama’, the most important of which being the following: 198 First: Which is the most important of all.
It includes the traditions fabricated and falsified by the Zanadiqah disguising cheatingly and hypocritically under the guise of Islam, with the purpose of corrupting and ruining the religion with creating conflict and disunity among Muslims. Hammad ibn Zayd said: The Zanadiqah have fabricated four thousand traditions.
This being the number he could realize through his knowledge and investigation in discovering their falsity, whereas the traditionists reported that only one zindiq had composed this number of traditions. They say that” When Ibn Ali al-Awja’ was taken to be beheaded, he said: “I fabricated for you four thousand traditions, forbidding in them the halal (lawful) and deeming lawful the haram (unlawful)”.
Second: Fabrication of hadith for the sake of backing and supporting the schools of thought in regard of principles (usul) and branches of religion. Since when Muslims were separated into schisms and madhahib, every group embarked on doing its utmost to prove the legality of its madhhab, especially after the door of debate and disputation regarding the madhahib was opened wide.
The aim of this was only dumbfounding the opponent and showing of superiority over him, to the extent they have made dispute a science compiling on it many works, though their religion was averse to nothing but to dispute and conflict. This cause seems to be one of the consequences and effects of the previous one.
This cause was cited by some of the traditionists who had written about causes of fabrication, saying: Someone among the heretics repented and embarked on expressing: You should investigate the source from which you take the hadith, as we used to render to a hadith whatever we desired or loved to be attained. Fabrication of hadith for supporting the madhahib was not restricted to the heretics and owners of schools in usul.
Rather many among Ahl al-Sunnah, who having disagreement about the branches (furu’) of religion, were known of composing traditions each for supporting one of the schools of thought or glorifying any of the leaders (imams)... I introduce here one hadith as an example: “There shall be a man in my Ummah called Muhammad ibn Idris, who will be more detrimental to my Ummah than Iblis.