Even in the lifetime of the holy Prophet...
Even in the lifetime of the holy Prophet, people did attribute false statements to him so such an extent that he himself stood up and addressed the people, 'O people, those who attribute false statements to me secures his abode in hell.' Then the people went on attributing false statements to him after his death. Whatever traditions you (people) have received are from four categories (of narrators). There is no fifth category.
The first is a hypocrite who poses himself as a believer and actually is a shame Muslim. Attributing false statements to the Prophet intentionally, is not considered by him as a sin, nor does he mind such an attribution. Were the people even to know how false and hypocritical he is, they would never accept a word from him, nor would they confirm his statements.
It was this type of man about whom people started saying, 'This is the one who had been honoured by the company of the Prophet and who has actually seen and heard the Prophet.' People accepted traditions from him without knowing his credentials. Allah the Almighty has told His Prophet about the hypocrites all that was to be told and has detailed all the characteristics that were to be detailed.
Allah the Almighty has said so, 'When you see them, you marvel at their personalities; and if they speak, you listen unto their speech.' (al-Munafiqun 63:4) 'Such people remained there after the Prophet as well. Then they got near the leaders (rulers) who misguided and invited people towards the hell fire through the means of their fabrications, falsehood and slander.
They were entrusted with big jobs by the rulers of the time and were thus foisted on the people, and their rulers exploited the situation through them. Except the few whom Allah saved, the common people were always with their rulers and with their mundane business of the world. All this is the description of the one out of all categories. (The second is the category of a person) who has actually heard something from the Prophet but was not able to retain it in his mind and fell into doubt.
He never intentionally told a lie, but he started speaking, practicing and propagating what he remembered incorrectly and sketchily, and at the same time claimed that 'I have heard the Prophet say so.' If the Muslim community had known that he was in error, they would never have accepted his words. And if the man himself had known that he was mistaken, he would have himself rejected his own version.