The sacred months in Islam

The sacred months are Dhul-Qi`dah, Dhual-Hijjah,Muharram, and Rajab. The name of Dhul-Qi`dah indicates in Arabic giving upfighting and traveling in preparation for the Hajj season. Dhul-Hijjah is called so because it is the month when Hajj takes place. Muharram is an emphatic form of tahrim, which indicates prohibiting vices and wrongdoings. Rajab is 
derived from the Arabic word tarjib, meaning glorification and esteem. Almighty Allah says about the sacred months: [Lo! The number of the months with Allah is twelve months by Allah'sordinance in the day that He created the heavens and the earth. Four of them are sacred: that is the right religion. So wrong not yourselves in them] (At-Tawbah 9:36).

The Prophet (peace and blessings be upon him) also said about them, "The division of time has turned to its original form which was current when Allah created the Heavens and the Earth. The year is of twelve months, out of which four months are sacred. Three are in succession: Dhul-Qi`dah, Dhul-Hijjah and Muharram, and (the fourth is) Rajab of
(the tribe of) Mudar which comes between Jumada Thani and Sha`ban" (Al-Bukhari).     

The Prophet (peace and blessings be upon him) described "RAJAB" as "(of the tribe of ) Mudar"because this tribe would locate this month correctly between Jumada Thani  and Sha`ban, unlike the tribe of Rabi`ah, which would refer to this sacred month as coming between Sha`ban and Shawwal, which, incorrectly, means it is Ramadan.
There was a long-established custom of observing those four months as those in which fighting is forbidden. The Pagan Arabs, however, might change those months about, transposing Muharram, for instance, to the month of Safar so that they might take at the former an unfair advantage overthe enemy who might (out of observing the sacred month) hesitate to fight. This is called an-nassi' (postponement [of a sacred month]). Almighty Allah says in this respect: [Postponement (of a sacred month) is only an excess of disbelief whereby those who disbelieve are misled, they allow it one year and forbid it (another) year] (At-Tawbah 9:37). 
These months have special advantages peculiar to them. For example, fighting is to be given up altogether during these months unless it is for self-defense. Rewards of good deeds are doubled and punishment for wrongdoings is multiplied. Moreover, Imam Ash-Shafi`i and many other scholars believe that blood money paid to the family of a victim killed
or injured during these months should exceed the amount given in other months. 
In explaining Allah's words [So wrong not yourselves in them] (At-Tawbah 9:36), the eminent scholar Qatadah said, "Wronging oneself or others is more sinful and wicked during the sacredmonths than in other ones, as Almighty Allah grants solemnity to whomever and whatever He Most High likes." 

Qatadah also said, "Almighty Allah chose of (the different kinds of) His creation [some] things and persons as having special places and importance than others (in His sight). He Most High chose from the angels -- messengers [to convey His divine messages, mercy, punishment, etc., to the worlds]; chose from discourse that which reminds of Him; chose from the places on the earth --> His mosques; chose from the months --> Ramadan and the sacred ones; chose from days --> Friday, and from nights --> the Night of Decree. So hold in high esteem that which Almighty Allah holds in high esteem."