Reciting the Qur’aan without pronouncing the letters properly.
Bismillaahir Raĥmaanir Raĥeem
I find many people today who recite the Qur’aan without paying any attention to the Makhaarij of its Ĥuroof, so they recite the Qur’aan as though it was revealed in Urdu or other such languages, where an `Ain and an Alif are pronounced the same, where a Thaa, a Seen and a Ŝaad are pronounced the same, where a Zaa, a Dhaal, a Zhaa and a Đaad are all pronounced the same, and this is a major problem which is taken far too lightly.
Imaam Badruddeen Al`Ayni Raĥimahullaah touches on this topic in Sharh Sunan Abi Daawood and he says:
If a person recites in his Ŝalaah “Alĥamdulillaah” with a haa, or “Ar-Raĥmaanir Raĥeem” with a haa, or “Ghayril maghđoobi `alayhim” with a daal, or “Qul a`oodhu” with a daal, or “Allaahuŝ Ŝamad” with a seen and so on, if such a person exerts himself day and night trying to correct it but is unable to do so, then his Ŝalaah is valid, because he is incapable of doing it, but if he does not exert himself then his Ŝalaah is invalid, because he is capable.
And if he has not strived to correct it in his early life, then that will not be an excuse for him to leave its correction for the remainder of his life, and if he leaves it then his Ŝalaah will be invalid, unless he tries continuously to correct it.
As for the lisper and stutterer, and those who are unable to pronounce certain letters due to a natural inability and so on, they are the ones who are excused by the Sharee`ah, so their Ŝalaah for themselves is valid, but none should follow them in Ŝalaah except those who are like them, for this case is like the case of an unlettered person who is unable to recite the Qur’aan.
End quote of Imaam Badruddeen Al`Ayni Raĥimahullaah.
May Allaah grant us all the ability the recite the Qur’aan the way it is meant to be recited.
Was Salaamu `Alaykum Wa Raĥmatullaahi Wa Barakaatuh.
 Instead of ĥaa ح.
 Instead of đaad ض.
 Instead of dhaal ذ.
 Instead of ŝaad ص.
 After trying his utmost.
 Because he has not tried to the best of his ability to correct it.
 Some people think that because they are old they do not have to bother striving to correct their makhaarijul ĥuroof , or they feel shy to learn at an advanced age, but this is not a valid excuse in the sharee`ah.
 i.e. they lisp or stutter or are unable to pronounce certain letters due to a natural inability.
 i.e. they cannot lead people in ŝalaah who can recite the Qur’aan, they can only lead people who are like them.