: All perfect praise be to Allah, The Lord of The Worlds; and may His blessings and peace be upon our Prophet Mohammad and upon all his family and companions.
The Sunnah is that the Imam or the person praying alone recites loudly during the two Rakhas of Fajir as well as the first two Rakahs of Maghrib and Isha`, and recites silently during other prayers. This is according to the view of the majority of the Muslim scholars: The Malikites, the Shafites, the Hanbalites and those who agree with them, because this has been confirmed by reporting. Al-Imam Ibn Qodamah (may Allah have mercy on him)said, "The Imam recites loudly during the Fajir prayer and the first two Rakhas of the Maghrib and Isha` prayers, because this is recommended by the majority of the jurists, Muslims haven’t disagreed about doing so at those instances, and in principle it was done by the Prophet (PBUH), as reported from the worthy ancestors." {Al-Moghni 1/569}.
However, the Hanafites view that reciting loudly is an obligation, not a Sunnah.In their book "Al-Hidayah (p.1/74)", they stated, "Even if the Imam recites loudly where he is supposed to recite silently or vice versa, he is obliged to offer the two Rakhas of forgetfulness, because loud and silent recitations in their supposed places are obligatory. Therefore, it wasn`t confirmed that any of the scholars has recommended reciting loudly where a person is supposed to recite silently or vice versa. Moreover, scholars have disagreed about the person who recited loudly where he is supposed to have recited silently or vice versa. The Hanafites and the Malikites said that he should prostrate for forgetfulness.
In their book "Al-Fawakeh Addawani (1/206)", the Malikites stated, "If a praying person recited loudly where he is supposed to recite silently or vice versa, then he should prostrate for forgetfulness after Tasleem." And Allah knows best.