Is it permissible to shun a person who clings to his innovation and argues without knowledge, or how should he be dealt with?

A Muslim may abandon (or shun) someone for the sake of religion, such as people of innovation (bid'ah), immorality (fisq), and transgression (fujoor), if a Sharia-compliant benefit results from it, like the innovator refraining [from their innovation] or people dispersing from them. Otherwise, they should not be abandoned.

However, if the Imam makes a grammatical error (laḥn) in Al-Fatiḥah that changes the meaning, then it is not permissible to pray behind him, except for someone who is like him. If the error does not change the meaning, then the validity of the prayer stands, but someone who recites better should not be put forward.

As for audibly reciting the adhkar individually after prayers, it is prescribed (mashroo'), unlike congregational supplication (du'a), which is an innovation (bid'ah). This latter [act] does not necessitate abandoning the Imam; rather, he should be advised, and one should pray behind him as long as his prayer is valid.