Is it permissible to perform six cycles (rak'at) of supererogatory prayer (salat al-nafl) after Maghrib, limiting the recitation to only Surat al-Fatiha?

The prescribed [Sunnah] after the Maghrib prayer is only two Rak'ahs of regular Sunnah (Ratibah). If someone prays more than that, there is no harm in it. The six Rak'ahs do not have a specific virtue, and no authentic Hadith has been reported concerning them. However, if someone performs them to increase in good deeds, there is no harm in it. The regular Sunnah that the Prophet consistently observed was only two Rak'ahs. If one prays them with only Al-Fatihah, it is sufficient, but it is better to recite along with it whatever is easy from the Qur'an.