What is the ruling on an imam who pronounces the letter "qaf" as "jim," the letter "ta" as "dad," and the letter "dad" as "zha," and refuses to correct his recitation? Is it permissible to pray behind him, and is it permissible to warn against him?

The imamate of someone who pronounces the letter Qaf as Jeem, or the letter Taa as Dhad, is not valid if they do so intentionally and are capable of learning, due to the difference in the points of articulation of these letters. It is obligatory to advise them and clarify their error. If they insist on the mispronunciation, prayer behind them becomes invalid, and their situation should be clarified to the worshippers.