What is the ruling on the prayer of someone who says in the Tasleem: "Peace be upon you and the mercy of God" without "al" (the definite article), and what are the implications for the congregants?

If the Imam intentionally omits the definite article "al-" from the tasleem (salutation), then prayer behind him is invalid according to the Malikis, and according to the more sound opinion among the Hanbalis and Shafi'is. However, if the Imam is unable to pronounce the definite article, then it is not permissible for someone who is not similarly afflicted to follow him. The congregants must avoid praying behind someone who intentionally does this, and whoever prays behind him after knowing that the tasleem is insufficient without the definite article, their prayer is nullified. As for the opposing view to the more sound opinion in the Shafi'i and Hanbali schools, and according to the Hanafis, the prayer of someone who gives the tasleem without the definite article is valid.