Is it permissible to pronounce the letter "ḍād" with "ishmām" as "ẓāʾ"?

If a worshiper is unable to distinguish between the Arabic letters "ḍād" (ض) and "ẓāʾ" (ظ), there is no sin upon him for pronouncing "ḍād" as "ẓāʾ". However, if he is able to learn and distinguish between them, then it is obligatory for him to do so, and he sins by neglecting it. His prayer is not invalidated unless he intentionally pronounces it incorrectly while being capable of pronouncing it correctly. Replacing "ḍād" with "ẓāʾ" in Al-Fatihah invalidates the prayer if the doer is capable, knowledgeable, and intentional. Some scholars view leniency regarding the precise distinction between them due to the proximity of their articulation points and the similarity of their characteristics. As for the hadith, "I am the most eloquent of those who spoke ḍād," it has no origin.