The Virtues of Allah's sacred month of Muharram and Fasting on 'Aashooraa'

What are the virtues of the month of Muharram and fasting 'Aashooraa'?

Praise be to Allaah, the Lord of the Worlds, and peace and blessings be upon our Prophet Muhammad, the Seal of the Prophets and Chief of the Messengers, and upon all his family and companions. Allah's sacred month of Muharram is a blessed and important month. It is the first month of the Hijri calendar and is one of the four sacred months concerning which Allaah says (interpretation of the meaning):

«Verily, the number of months with Allaah is twelve months (in a year), so it was ordained by Allaah on the Day when He created the heavens and the earth; of them, four are sacred. That is the right religion, so wrong not yourselves therein.» [al-Tawbah 9:36]