Is the beginning of the day Fajr or Maghrib, and what is the Middle Prayer?

The 'Middle Prayer' (Salat al-Wusta) is a matter of scholarly disagreement, with two main opinions: the Dawn Prayer (Fajr), which is the view of Abu Umamah, Anas, and others, and was chosen by Malik and Al-Shafi'i; and the Asr Prayer (Afternoon Prayer), which is the view of Ali ibn Abi Talib and most scholars, and is the correct, relied-upon opinion. The evidence for the second opinion is the Prophet's (peace and blessings be upon him) statement on the Day of al-Ahzab (the Confederates): "They distracted us from the Middle Prayer, the Asr Prayer." Al-Dumyati mentioned specific characteristics for the Asr Prayer, such as the immense calamity of missing it and the invalidation of the deeds of one who abandons it. As for the beginning of the day, night precedes day, but this does not necessitate that Fajr is the 'Middle Prayer'; rather, what is meant by 'Middle Prayer' is the most virtuous prayer.