Allah says (interpretation of the meaning): “Verily, the number of months with Allah is twelve months (in a year), so was it ordained by Allah on the Day when He created the heavens and the earth; of them four are Sacred, (i.e. the 1st, the 7th, the 11th and the 12th months of the Islamic calendar). That is the right religion, so wrong not yourselves therein” [Soorat at-Tawbah 9:36].
It was narrated from Abu Bakrah (may Allah be pleased with him) from the Prophet (blessings and peace of Allah be upon him): “… The year is twelve months, of which four are sacred: three consecutive months, Dhu al-Qa‘dah, Dhu al-Hijjah and Muharram, and Rajab of Mudar which comes between Jumaada and Sha‘baan.” Narrated by al-Bukhaari (2958).
These months are called sacred for two reasons:
1- Because fighting therein is forbidden unless initiated by the enemy
2- Because transgression of the sacred limits therein is worse than at other times.
Hence Allaah has forbidden us to commit sins during these months, as He says (interpretation of the meaning): “wrong not yourselves therein”[al-Tawbah 9:36]
It was narrated that Ibn ‘Abbaas said, concerning the words of Allah “so wrong not yourselves therein” [Soorat at-Tawbah 9:36]: (The command not to wrong yourself) applies in all months, then Allah singled out four months and made them sacred, and emphasised their sanctity, and He made sin during these months more grave, and He made righteous deeds and the reward thereof greater.
Allah has chosen elites from His creation: from among the angels He chose Messengers, from among mankind He chose Messengers, from among speech He chose remembrance of Him (dhikr), from among spaces on earth He chose the mosques, from among the months He chose Ramadan and the sacred months, from among days He chose Friday (Jumu‘ah), and from among nights He chose Laylat al-Qadr. So venerate that which has been chosen by Allah, for people of understanding and wisdom respect that which has been chosen by Allah. End quote from Tafseer Ibn Katheer (may Allah have mercy on him), commentary on Soorat at-Tawbah verse 36
The virtue of observing a great deal of naafil (supererogatory) fasts during the month of Muharram. It was narrated that Abu Hurayrah (may Allah be pleased with him) said: The Messenger of Allah (blessings and peace of Allah be upon him) said: “The best fast after Ramadan is in the month of Allah Muharram.” Narrated by Muslim (1982).