What is the ruling on praying behind an Imam who does not recite Al-Fatihah well and pronounces the letter "Nun" as "Mim" when pausing on it, bearing in mind the difficulty of going to another mosque?

If the Imam recites "nasta'in" as "nasta'im," this is a substitution of one letter for another, which is impermissible and considered a grammatical error (laḥn) that alters the meaning. This makes the Imam unqualified to lead a skilled reciter in prayer. So, if someone substitutes one letter for another in Al-Fatiḥah, like a lisping person, or commits a grammatical error that alters the meaning, it is not permissible for him to lead a skilled reciter in prayer. If the Imam is unable to learn, his prayer for himself is valid, and some jurists hold that following him in prayer is also valid. The matter should be brought to the Ministry of Endowments to replace him with someone suitable for leading the prayer. If the questioner is female, it is preferable for her to pray at home, as her prayer at home carries a greater reward for her.