What is the ruling on the prayer led by an Imam who recites "ghayril maghdoubi" with an "a" sound on the letter baa (بِ), and extends his tongue moderately when pronouncing the letter Dhad (ض) in the words "al-maghdoubi" and "al-dhaalleen," knowing that there is no defect in his tongue?

Changing the letter "ḍād" to "ẓāʾ" is not permissible. However, for many common people, their prayer is not invalidated by it due to the difficulty in distinguishing between the two, unless one intentionally does so despite being able to pronounce it correctly; in which case, he commits a sin and his prayer, as well as the prayer of those who follow him, becomes invalid. As for an error in recitation (laḥn), if it does not alter the meaning, then the prayer is valid, though disliked. But if it alters the meaning, then whoever commits it intentionally or is negligent in learning it commits a sin, and his prayer becomes invalid, and it is not permissible to follow him in prayer.