What is the ruling on letters that do not appear clearly when reading silently in prayer, such as the letter "dal" that comes out as if it were a "ta" in the word "yawm ad-din"?

Hidden recitation whispers are a form of waswasa (whispers from Satan), especially if the recitation is correct when recited aloud. Do not pay attention to them, and do not recite aloud except where it is prescribed.

Ibn al-Jawzi held that Iblis misleads some worshippers regarding the articulation points of letters, leading to exaggeration in their pronunciation, which distracts them from understanding the recitation.

Ibn al-Qayyim also emphasized that excessive meticulousness and affectation in articulating letters are not part of the Sunnah of the Prophet, peace and blessings be upon him.

It is prescribed for a woman to recite aloud in the appropriate places such that she can hear herself and those next to her, except in the presence of non-mahram men, in which case she should recite silently for fear of fitna (temptation).