What is the ruling on the prayer of an Imam who errs in Surat Al-Fatihah, in His saying, the Almighty: "the path of those upon whom You have bestowed favor" by merging the letter Noon in "الذين" (those) with the letter Noon in "أنعمت" (You have bestowed favor), thus becoming "الذينّعمت" with the omission of the hamza, and what is the ruling on the prayer of the congregants behind him, knowing that he has not corrected his error despite being alerted?

Reciting Al-Fatiha is one of the pillars of prayer. Whoever omits a letter from it, their recitation is not considered valid. It is not permissible for a reciter to pray behind someone who omits a letter from Al-Fatiha due to inability, or substitutes it, or merges one letter into another. The Shafi'is in their new opinion, most Hanbalis, and also the Hanafis, have gone to the extent of deeming it invalid to pray behind someone who is tongued-tied (al-alkan) and omits a letter from Al-Fatiha, or substitutes it, or generally cannot pronounce certain letters. If the tongued-tied person is able to correct their tongue and ceases to make these errors, and yet continues to do so, their prayer is invalid and it is not permissible to pray behind them. However, if they are unable to correct themselves, then their prayer is valid and it is permissible for someone in a similar situation to pray behind them. Based on this, it is not permissible to pray behind a person who omits a letter from Al-Fatiha, and the able follower must repeat their prayer. As for the prayer of the tongued-tied person themselves, it is valid if their tongue does not enable them to correct their pronunciation.