Is salat valid if the imam’s recitation is incorrect and the follower knows the sura correctly?

Assalamualikum My question is regarding the repeating salat. Shaik, whats the masala for praying salat behind an imam who’s recitation is not correct. Like, sura fatiha is not correct and other sura as well. More precisely, what if his pronunciation of the alphabets is incorrect. Besides, if someone omits the huruf al-madm in the recitation during the salat, is salat valid for the person who is following the imam. Provided that one who is follwing the imam, knows the sura correctly. Does he need to repeat his salat? Particularly Magrib, Esha & Fajr. This kind of problem arises, when I go for second Jula in other location. Sometimes, it is very hard to repeat the salat during the Magrib time. Because, our jula starts after Magrib salat. I have hard that salat will be valid if someone’s recitation is correct at least three ayat in rakah. How do we have to count three ayats. Do we have to count the three ayatsafter the sura fatiha? or it includes sura fatiha with any sura? I will be glad to hear from you. Jazakallah khir