Praying Behind an Imam Who Practices Witchcraft?

Almighty Allah says:

And they followed [instead] what the devils had recited during the reign of Solomon. It was not Solomon who disbelieved, but the devils disbelieved, teaching people magic and that which was revealed to the two angels at Babylon, Harut and Marut. But the two angels do not teach anyone unless they say, “We are a trial, so do not disbelieve [by practicing magic].” (Al-Baqarah 2:102) 

Sheikh Ibn Baz (may Allah have mercy on him) was asked:

Is it permissible to pray behind an Imam who is a charlatan and a liar, knowing that some of them recite Qur’an well?

He replied:

“If the Imam is a charlatan who claims to have knowledge of the unseen or who does false and evil things, then it is not permissible to appoint him as an Imam for prayer or to pray behind him. Allah says (interpretation of the meaning):

Say, “None in the heavens and earth knows the unseen except Allah, and they do not perceive when they will be resurrected.“ (An-Naml 27:65)

To know more about the ruling of offering prayer behind one who practices sihr (witchcraft or magic), watch this interesting talk with Dr. Muhammad Salah.