I have a question about the salah. If the Prophet (sws) offered salah in different ways then how can Hanfis, Hanbalis, Shafi'is and Malikis insist on their set ways? Is not it a bid'ah?
There is no significant variation in the necessary parts (rituals as well recitations) of salah. The Prophet (sws) taught salah prayer to the entire generation of the believers. As a result the basic form and components of the ritual are agreed upon by all. The issues subject to difference are few. They pertain only to areas where the Prophet (sws) left the believers with an option to choose from two or more possible ways. Later on people started to follow one option and declared the other wrong. This is not a positive behavior. Where the Prophet (sws) did not legislate and determine a set course of action people should be allowed to adopt any of the available options. Strict adherence to one's own preferred view where there is an option open leads to sectarianism and blind following.