What is the ruling on pulling back a person who has stepped forward to lead the prayer (Imamah) but is not proficient at it, so that someone more qualified can take his place, and how should we deal with an Imam who makes a grammatical error (laḥn) in Al-Fatihah that changes its meaning, or does not pray with tranquility (ṭumaʾnīnah), and is it permissible to pray behind him, or must the prayer be repeated?

If someone whose leadership is invalid comes forward to lead the prayer (Imamah), then his leading is a reprehensible act (Munkar) that must be changed. This should be done by hand, by delaying him if possible, without causing mischief. Otherwise, it should be done by speech. It is not permissible to pray behind him while knowing his condition, because the prayer would be invalid. His case should be reported to the relevant authorities. However, if his leadership is valid, even if disliked, then it is permissible to pray behind him.