What is the ruling on praying behind someone who unduly prolongs the pronunciation of the letter "Lām" in the Takbir or in Al-Fatihah?

The repetition of the letter "lām" in the word for Allah (Jalalah) or excessive emphasis on it is disliked but does not invalidate the prayer, unless the meaning is changed. Excessive prolongation of vowels can turn them into letters. Similarly, excessive stillness of the "lām" in the word "al-mustaqīm" (the straight) does not invalidate the prayer. For someone who repeats a letter from Al-Fatihah, their imamate (leading of prayer) is disliked, but their prayer is valid. Some jurists hold the view that repeating a letter invalidates the prayer if it causes an addition that changes the meaning.