Muharram is the month with which the Muslims begin their lunar Hijrah Calendar. It is one of the four sanctified months about which the Holy Quran says, "The number of the months according to Allah is twelve (mentioned) in the Book of Allah on the day He created heavens and the earth. Among these (twelve months) there are four sanctified."

These four months, according to the authentic traditions, are Dhul-Qa'dah, Dhul-Hijjah, Muharram and Rajab. All the commentators of the Holy Quran are unanimous on this point, because the Holy Prophet (Peace Be Upon Him), in his sermon on the occasion of his last Hajj, declared: "One year consists of twelve months, of which four are sanctified months, three of them are in sequence; Dhul-Qa'dah, Dhul-Hijjah, Muharram, and the fourth is Rajab."
The specific mention of these four months does not mean that any other month has no sanctity, because the month of Ramadan is admittedly the most sanctified month in the year. But these four months were specifically termed as sanctified months for the simple reason that their sanctity was accepted even by the pagans of Makkah.

In fact, every month, out of the twelve, is originally equal to the other, and there is no inherent sanctity that may be attributed to one of them in comparison to the other months. When Allah Almighty chooses a particular time for His special blessings, the same acquires sanctity out of His grace.
Thus, the sanctity of these four months was recognized right from the days of Sayyidina Ibrahim, alayhi salam. Since the Pagans of Makkah attributed themselves to Sayyidina Ibrahim, alayhi salam, they observed the sanctity of these four months and despite their frequent tribal battles, they held it unlawful to fight in these months.

In the Shariah of our Noble Prophet (Peace Be Upon Him), the sanctity of these months was upheld and the Holy Quran referred to them as the "sanctified months".

Muharram has certain other characteristics special to it, which are specified below:
Fasting During the Month
The Day of 'Ashurah'
Misconceptions and Baseless Traditions
Lamentations and Mourning.
 
Fasting During the Month:
The Noble Prophet (Peace Be Upon Him), has said: "The best fasts after the fasts of Ramadan are those of the month of Muharram."
Although the fasts of the month of Muharram are not obligatory, yet one who fasts in these days out of his own will is entitled to a great reward by Allah Almighty. The Hadith cited above signifies that the fasts of the month of Muharram are most rewardable ones among the Nafl or voluntary fasts.
The Hadith does not mean that the award promised for fasts of Muharram can be achieved only by fasting for the whole month. On the contrary, each fast during this month has merit. Therefore, one should avail of this opportunity as much as he can.