that is a common misunderstanding, Hadiths were known and said by people since the death of Mohammed , But Bukhari and Muslim may be the first scholars who invented what is called Al Jarh wa Al tadil and put some standards and rules to give different grades to Hadiths as we discussed before the Sahih (sound), Good (hasan) and Weak.<quoted text>
Bukhari & Muslim were 9th century scholars and they were the ones who compiled the hadiths. How of those hadiths they compiled were fabricated? No one knows for sure. Oral tradition is not history despite the fact they could contain elements of truth in them.
So hadiths were there dafinetly but with no grades.