Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions. It is proved from Prophet Muhammad (Sallallahu Alaihi wa Sallam) that he ordered to recite the Muawwazat (last three Surahs of the Qur'an; 112, 113 and 114) after the end of every prayer of the five daily obligatory prayers. Imam Ahmad in his book "al-Musnad" and other reported from Uqbah Bin Aamir that The Prophet (Sallallahu Alaihi wa Sallam) ordered him to recite the three last Surah of the Qur'an after every prayer . Sheikh al-Albani and al-Arnaood graded this Hadith as sound. This Hadith is common so, those Surahs should be recited after all five prayers not only after Maghrib or Fajr prayers. As for reciting the last three Surahs after Fajr and Maghrib prayers, we do not find any evidence for that. However, there are sound evidences that prove that those Surahs should be recited thrice in the morning and in the evening. The Prophet (Sallallahu Alaihi wa Sallam) said: Recite Surah al-Ikhlas and two last Surahs of the Qur'an, in the morning and evening three times, and it will suffice you for everything . [ Abu Dawood and al-Tirmizi ] Thereupon, reciting those Surahs after 'Asar because it is the time when the evening starts and after Fajr when the morning starts is permissible. It is also said that the evening starts from Maghrib and in that case the Azkar that should be recited during evenings are recited then. Allah knows best.