Praying behind a person who pronounces Dhaad as Thaa’
11-11-2015 | IslamWeb
Question:
Assalaamu alaykum wa rahmatullaahi wa barakaatuh. What is the correct 'makhraj' and method of pronunciation for the letter ض? What is the ruling on praying behind a person who pronounces it as 'zwaad' or like the letter ظ?
Answer:
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ʻalayhi wa sallam, is His slave and Messenger.
If you wish to identify the makhraj (point of articulation) and characteristics of the letter Dhaad (known as the empathic “D” and the 15th letter of the alphabet) or any other letter, then you should learn them through direct instruction at the hands of a specialized Tajweed teacher. There is no real benefit in reading Tajweed books or theoretical Fataawa on that subject unless accompanied by practical implementation of the explained rules by a qualified Tajweed teacher, especially pertaining to the proper pronunciation of the letter Dhaad and the letter Thaa’ (the 17th letter of the alphabet) because they share many characteristics and given the difficulty of differentiating between them for many people. Allaah, The Exalted, willed that the proper recitation of the Quran is learned through direct oral instruction and not through any other means. This is why Allaah says to His Messenger 
(what means): {So when We have recited it [through Gabriel], then follow its recitation.} [Quran 75:18]
If you wish to identify the makhraj of any letter, then try pronouncing it in a state of Sukoon (absence of a vowel sound) or Shaddah after a Hamzat Wasl (non-phonemic glottal stop). At the point where the sound stops, that is the makhraj of the letter.
Hence, if we pronounce the letter Dhaad with Sukoon after a Hamzat Wasl, the sound stops at the side of the tongue and the adjacent molars. That is why the Tajweed scholars said, “The makhraj of the Dhaad is the side of the tongue and the molars on one side or both.”
As for the person who pronounces the Dhaad like the Thaa’, his prayer performed individually is valid and if he leads the prayer, the prayer of the led is valid as well according to some scholars. This is considered the preponderant view according to Ibn Taymiyyah 
. He wrote in relation to this topic:
“... The second scholarly view holds that the prayer (of a person behind an Imaam who says Ath-Thaalleen instead of Adh-Dhalleen while reciting al-Faatihah) is valid. This is the most likely view given that the two letters (Dhaad and Thaa’) sound similar because of the similarity between the two makhrajs of both of them. When the worshipper alters one letter for the other; pronouncing Ath-Thaaleen instead of Adh-Dhaalleen, he means misguidance and the listener can easily realize the intended meaning, while the wrong meaning (of Ath-thaalleen, i.e. those who continue to do something) does not cross the listener’s mind ... This is different from substituting a letter for another one that is totally different in terms of sound, makhraj and pronunciation (as in the case of the letter Raa and the letter Ghayn in the word Rabb, for example, by saying Ghabb instead of Rabb).” [Majmoo’ Al-Fatwaawa]
Imaam Ibn Katheer wrote:
“The correct scholarly view in this regard is that mild defective pronunciation in case of changing the Dhaad for the Thaa’ is pardoned given the proximity of their makhraj. The letter Dhaad is pronounced from the side of the tongue and the molars. The letter Thaa’, on the other hand, is pronounced from the tip of the tongue and the edges of the two front upper teeth. Since both letters share the same characteristics: Jahr (audibility; voiced letters which traps air flow due to heavy reliance on the makhraj), Rakhaawah (weakness or softness; the flowing of sound upon pronunciation), and Itbaaq (closing; compression of the sound between the tongue and the roof of the mouth), alternating one of them for the other is pardoned for he who cannot distinguish their different makhraj and accordingly substitutes one of them for the other in pronunciation...” [Tafseer Ibn Katheer]
Allaah Knows best.