What is the ruling on the prayer of those led by an Imam who makes a mistake in reciting Surat Al-Fatihah by saying "اهدني الصراط المستقيم" (Guide me to the straight path) instead of "اهدنا الصراط المستقيم" (Guide us to the straight path)?

The error mentioned is a clear grammatical mistake (laḥn jalī) that alters the meaning of the noble verse. It is not permissible to follow the one who committed it in prayer unless he corrects it. Therefore, those who prayed behind him must repeat their prayers, and he must correct his error if he is able. If he leads the prayer with this error while being able to correct it, his prayer is invalid.