Oldest Evidence Says Hadiths were Fake

A letter from Kharijite Abd Allah Ibn Ibad (d.c. 86/705) to Caliph Abd Al Malik (r.65/685-86/705) predating Al Shafi'i has the following passage about Kufans who happen to be the hadith scholars.

"They abandoned the judgement of their lord and took hadiths for their religion; and they claim that they have obtained knowledge other than from Quran."

"They believed in a book which was not from God, written by the hands of men; they then attributed it to the Messenger of God."

The words are translated by Michael Cook in his Early Muslim Dogma: A Source Critical Study (Cambridge: Cambride University Press, 1981, 66-67.