Imam Ibn Rajab Al-Hanbali (d. 795 AH), may Allah be pleased with him, declared about the first month, Muharram:
And because of this it is said that the fasting the six days of the month of Shawwal are connected to the month of Ramadan and it is written that whoever fasted them along with Ramadan is like fasting the entire year of compulsory fasts
It is narrated that Usamah ibn Zaid used to fast the holy months so the Prophet, peace and blessings of Allah be upon him, commanded him to do the fast in Shawwal and so Usamah left fasting the holy months and fasted Shawwal.
We will mention the fasting in the month of Shawwal when it is time, if Allah, Exalted be He, wills. This particular branch of fasting is connected to Ramadan and its fasting is better than other fasts in general.
As for the general fast, then the best of these general fasts are the holy months. It was collected in a hadith from the Prophet, peace and blessings of Allah be upon him, commanded a man to fast the holy months.
And we shall mention this in another place when it is time, if Allah, Exalted be He, wills. The best fast one could do in the holy months is the Fast of the Month of Allah in Al-Muharram.
So this is testified to that he, peace and blessings of Allah be upon him, said in this hadith, “The best prayer after the compulsory prayer is qiyam ul-lail.” So the intent of the statement ‘after the compulsory prayers’ means after he has established the regular optional prayers associated with the compulsory prayers, whether before them or after.
These regular optional prayers are nobler and more virtuous than qiyam ul-lail according to the majority of scholars due to their relation to the compulsory prayers. It is only some of the Shafi`iis that have an opposing position.
And likewise the fast before Ramadan and after it is connected to Ramadan and its fast is better than the fast in the holy months. The best general optional fast is the fast of Al-Muharram.
The scholars differ with regard to which of the holy months is the most virtuous and noble. Al-Hasan Al-Basri and others said that the best of the holy months is the Month of Allah, Al-Muharram. And this was the preferred position of a group of latter day scholars.
Wahab ibn Jarir narrated from Qurrah ibn Khalid from Al-Hasan Al-Basri who said, “Indeed Allah opened the year with a holy month and closed it with a holy month. There is no month in the year after the month of Ramadan more immense in the Sight of Allah than Al-Muharram.”
Allah gave the month this name on account of the stringency and severity of its holiness. It was collected in an attributable hadith and a singular hadith from Adam ibn Abi Iyyas: It was narrated to us by Abu Hilal Ar-Rasi from Al-Hasan Al-Basri who said that the Messenger of Allah, peace and blessings of Allah be upon him, declared, “The best prayer after the compulsory prayer is the one in the middle of the night. The best of months after the month of Ramadan is Al-Muharram and it is the Month of Allah.”
Source: Lata’if ul-Ma`arif Fima Li-Mawasim il-`Ami Min Al-Waza’if, pp. 35-38