وَالْإِسْرَارُ فِي الظُّهْرِ وَالْعَصْرِ، وَفِيمَا بَعْدَ أُولَيَيِ الْعِشَاءَيْنِ، وَنَفْلِ النَّهَارِ، وَالْمُنْفَرِدُ مُخَيَّرٌ فِيمَا يَجْهَرُ
Silent recitation is Wajib in:
• Zuhr and Asr;
• the third rak'ah of Maghrib and the third/fourth of Isha;
• daytime Nafl prayer.
A solitary worshipper has a choice in prayers in which an Imam would recite aloud, similar to a person praying Nafl at night.