Is it obligatory to advise someone who raises their voice during a silent prayer after they have finished, and is their action considered a reprehensible act?

If someone recites aloud in a silent prayer, their prayer is valid. It is recommended, but not obligatory, to advise them, as they have not committed anything unlawful. Therefore, enjoining good in a recommended matter is itself recommended.

However, if their loud recitation disturbs other worshippers, it becomes obligatory to stop them from this wrong action. No one should recite aloud, whether in prayer or otherwise, if others are praying in the mosque and they are disturbed by the loud recitation. This is based on the Prophet's (peace and blessings be upon him) saying: "O people, each of you is supplicating his Lord, so do not raise your voices over one another in recitation." These two hadiths prohibit reciting aloud in prayer when it causes disturbance to others, indicating that this causes harm which is forbidden.