The later generations who lorded over the Sunnah instead of submitting to it:

Then there came after them a generation that squandered and neglected the Prophetic Sunnah because of certain principles adopted by some ʿulamaʾ al-kalām (speculative theologians) and rules claimed by some ʿulamaʾ al-uṣūl and muqallid jurists. The result of those principles was precisely the neglect just mentioned: it led to doubting a large portion of the Sunnah and to rejecting another portion on the grounds that it conflicted with those principles and rules. Thus the whole affair was reversed for them; instead of returning to the Sunnah and seeking its judgment, they turned the matter on its head