The ruling on praying behind one who mocks the people of the Sunnah and attends religious innovations

Question:
Honorable Shaykh, may Allah grant you success. The questioner says: I have an imam who leads the gatherings and ascends the pulpit, but he often mocks the people of the Sunnah in his sermons, and he lets his garments hang below his ankles. I have advised him, and he attends the innovated celebrations. He says: What is your advice regarding this, and what is my position toward him?

Answer:
Advise him. If he does not comply, then you advise the congregation. You say: Look, this is not suitable for the role of imam; this is such and such, and if such and such, you advise the congregation.