‘Correct his Speech According to his Own Language’
Hazrat Ubayy (ra) would teach the Holy Quran to an Iranian in the blessed era of the Holy Prophet (sa). When he taught him the verse,
إِنَّ شَجَرَةَ الزَّقُّوْمِ طَعَامُ الْأَثِيْمِ
The Iranian was not able to properly pronounce the word “atheem” [sinners] and whenever he would recite the word atheem, he would recite it as yateem. Hazrat Ubayy (ra) was very concerned as to how he could teach him. The Holy Prophet (sa) happened to be passing by and seeing the concern on the face of Hazrat Ubayy (ra), he stopped. When he heard the discussion he said in Persian, “Try saying it as طَعَامُ الظَّاثِمْ [ta‘amun zathim] this is with a ظ [zaa]. When he tried reciting it in this manner he very clearly said اثيم [atheem]. Thus, when Hazrat Ubayy (ra) read out ظَاثِمْ [zathim] and the Iranian replied saying اثيم [atheem] and was able to pronounce it correctly.
Thereupon, the Holy Prophet (sa) said to Hazrat Ubayy (ra), “Correct his speech according to his own language so that he may learn to recite the Holy Quran correctly, and ensure he pronounces the letters fully, God Almighty will reward you for this.”
(Sheikh Shah Moinuddin Ahmad Nadvi, Siyar al-Sahabah, Vol. 3 [Karachi, Pakistan: Dar al-Ishaah Urdu Bazar, 2004] 152)