Assalamualaikum ustaz. What is the ruling if a person recited “ولا الظالين” in surah al-Fatihah, when it is supposed to be recited “ولا الضالين” (with the letter ‘ض’)?
Alhamdulillah, praise and gratitude to Allah SWT for His countless blessings for us all. Praise and salutations to our beloved Prophet Muhammad PBUH, his family, companions and all those who follow his footsteps until the Last Day.
Regarding this issue, the recitation of “ولا الظالين” is not stated or it is not included in the mutawatirah qiraat (well-known/universally known recitation). Hence, it is included in the syaz qiraat (unusual) for the syaz qiraat is the qiraah (recitation) that is the opposite of mutawatirah qiraat. In this issue, Imam al-Nawawi once said: “It is impermissible to recite (al-Quran) in prayer or other than it with the qiraah (recitation) that is syaz for it’s not from al-Quran. The reason is al-Quran is not sabit except what is tawatur (mutawatir).” 
According to the above question, here we cite some of the fatwa from Syeikh Athiyyah Saqar when he was asked regarding the ruling of changing the letter Dha (ض) with the letter Zho’ (ظ) in the Quran and is it permissible to follow an imam who recites “ولا الظالين” which is different from the correct recitation which is “ولا الضالين”.
He explained that the correct recitation for the letter (ض) is not the same as the correct recitation for the letter (ظ) although both letters are similar in most of their attributes except Dho’ is different from Zho’ in terms of their makhraj and istitholah attributes.
As for the ruling of changing a certain letter with another letter in the Quran in prayer, the scholars stated: If it is done intentionally in a situation where he knows the difference between both the letters, then it is prohibited. Furthermore, some scholars state that it is kufr (disbelief/renouncing Islam) for it is considered as changing the Quran. Hence, his prayer is invalid and also if following him (if he is the imam).
If it is done unintentionally (in ignorance), then it is obligatory for him to learn and try his best to understand the correct way of pronouncing the letter. If he didn’t (pronounce it correctly) when he is capable, then his prayer is invalid as well as following him. However, if he is incapable or isn’t able to correct his pronunciation, then his prayer is valid as well as following him (he is the imam) as stated by the jumhur of fuqaha’. 
Likewise, it is as stated by Imam al-Nawawi in his book: “If changing the letter Dho’ (ض) and Zho (ظ) for the validity of his recitation and prayer, there are two opinions by Imam Abi Muhammad al-Juwaini and Imam al-Haramain, al-Ghazali has said in al-Basith as well as al-Rafi’ie and others, the more sahih between the two opinions is that it is invalid and this is the opinion held by al-Qadhi Abu al-Thib and Syeikh Abu Hamid, it is the same for changing the letter for another letter (which are Dho’ and Zho’). The second opinion is that it is valid due to difficulty to pronounce according to their makhraj for the general public and others like them.” 
According to the above fatwa and opinion, we are inclined towards the opinion that it is invalid for the prayer of a person who changes the letter in the recitation if it is done intentionally and one cannot follow an imam who recites the Quran as such except if the person isn’t capable to correct his recitation due to certain unavoidable reasons after he has tried his best. Thus, we advise a person to try his best to correct each word that is recited in the Quran with a teacher.
Hopefully, our Fatihah recitation truly follows the tajwid and what has been talaqqi from masyaikh until it reaches back to Rasullullah PBUH.