The recitation of Prophet Muhammad ﷺ out loud or silently is a Sunnah and not Wajibaat. If you are reciting outloud in Dhohr and Asr and then silently in Maghrib and Isha. It is obviously a Sunnah and we need to try to follow it.
When it comes to nafl prayers it is better to follow the pattern of Prophet ﷺ he would recite out loud during the night and silently during the day. However, there are some specific exceptions.
Shaykh Omar Suleiman answers and explains...
No transcription found