Allah’s has made Muharram sacred, as it is a blessed and important month; because:
1) It is the first month of the Hijri calendar.
2) It 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]
Abu Bakr (may Allaah be pleased with him) reported that the Prophet (sa) said:
“The year is twelve months of which four are sacred, the three consecutive months of:
2. Dhu’l-Hijjah and
3. Muharram, and
4. Rajab Mudar which comes between Jumaada and Sha’baan.” (Reported by al-Bukhaari, 2958).
3) Muharram itself also means sacred and confirms its sanctity.
4) The 10th of Muharram is the “day of Ashura”
Al-‘Izz ibn ‘Abd al-Salaam (may Allaah have mercy on him) said: “Times and places may be given preferred status in two ways, either temporal or religious/spiritual. With regard to the latter, this is because Allaah bestows His generosity on His slaves at those times or in those places, by giving a greater reward for deeds done, such as giving a greater reward for fasting in Ramadaan than for fasting at all other times, and also on the day of ‘Aashooraa’, the virtue of which is due to Allaah’s generosity and kindness towards His slaves on that day…” (Qawaa’id al-Ahkaam, 1/38).
5) Sins in this month are more serious, and good deeds bring greater reward
It was reported that Ibn ‘Abbaas said: Allaah’s words (interpretation of the meaning): “so wrong not yourselves therein…” referred to all the months, then these four were singled out and made sacred, so that sin in these months is more serious and good deeds bring a greater reward.
6) Virtues of observing Nafl (voluntary fasts)
Abu Hurayrah (may Allaah be pleased with him) said: “The Messenger of Allaah (sa) said: ‘The best of fasting after Ramadaan is fasting Allaah’s month of Muharram.’” (reported by Muslim, 1982).
The phrase “Allaah’s month”, connecting the name of the month to the name of Allaah in a genitive grammatical structure, signifies the importance of the month. Al-Qaari said: “The apparent meaning is all of the month of Muharram.” But it was proven that the Prophet sa) never fasted any whole month apart from Ramadan, so this hadeeth is probably meant to encourage increasing one’s fasting during Muharram, without meaning that one should fast for the entire month.”
It was reported that the Prophet (sa) used to fast more in Sha’baan. It is likely that the virtue of Muharram was not revealed to him until the end of his life, before he was able to fast during this month. (Sharh al-Nawawi ‘ala Saheeh Muslim).