✅Answer: According to narrations, the recitation of the Dhuhr and Asr prayers is done quietly (ikhfat) and the recitation of the Fajr, Maghrib, and Isha prayers is done loudly (jahr). Now, if a person does not observe the loudness and quietness in the prayers, this action can be intentional, or due to absent-mindedness and inadvertence, or due to forgetfulness, or due to ignorance.

The following narration specifies the ruling for all of these situations:

مُحَمَّدُ بْنُ عَلِیِّ بْنِ الْحُسَیْنِ بِإِسْنَادِهِ عَنْ حَرِیزٍ عَنْ زُرَارَةَ عَنْ أَبِی جَعْفَرٍ فِی رَجُلٍ جَهَرَ فِیمَا لَا یَنْبَغِی الْإِجْهَارُ فِیهِ وَ أَخْفَی فِیمَا لَا یَنْبَغِی الْإِخْفَاءُ فِیهِ فَقَالَ أَیَّ ذَلِکَ فَعَلَ مُتَعَمِّداً فَقَدْ نَقَضَ صَلَاتَهُ وَ عَلَیْهِ الْإِعَادَةُ فَإِنْ فَعَلَ ذَلِکَ نَاسِیاً أَوْ سَاهِیاً أَوْ لَا یَدْرِی فَلَا شَیْ ءَ عَلَیْهِ وَ قَدْ تَمَّتْ صَلَاتُهُ

📚Man La Yahduruhu al-Faqih, Vol. 1, p. 344

Translation: Imam Baqir (peace be upon him) said about a person who recites loudly where it is not appropriate to be loud, and recites quietly where it is not appropriate to be quiet: If he does either of these two things intentionally and with purpose, he has invalidated his prayer and it is his duty to repeat the prayer. And if he does this out of forgetfulness or inadvertence and absent-mindedness or out of ignorance, there is nothing upon him and his prayer is complete and correct.

✅It is observed that only in the case of intentionally abandoning the loudness and quietness in the recitation is it necessary to repeat the prayer, and in other situations, there is no need to repeat the prayer, and there is no other duty on us.

✅Sometimes a person does not observe the loudness and quietness in a part of the recitation due to forgetfulness and inadvertence, which according to the above narration has no problem, but whenever he becomes aware, he must observe the loudness and quietness in the rest of the recitation.