What is the ruling on praying behind someone who alters the form of the Tasleem, or does not pronounce the letter "hā" in the word "Allah"? And what is incumbent upon the worshipper in this situation?

Scholars have differed regarding the validity of the prayer of one who omits the definite article "al-" from the tasleem. The most correct view in the Shafi'i and Hanbali madhhabs is that it is not sufficient, while some have permitted it. Therefore, if someone intentionally omits the definite article in the tasleem, prayer behind him is not valid according to those who deem it insufficient. If someone is unable to pronounce the definite article, it is not permissible to follow him in prayer. As for not pronouncing the "ha" sound clearly in the name of Allah (Jalla Jalaluh), it does not affect the validity of the prayer as long as no letter is omitted or replaced. The imam should be advised gently to correct his mistakes.