There are differences between the so-called blessed months Rajab, Shaban, Ramadan and the haraam months mentioned in the Qur’an. Since it is forbidden (haraam) to make war on Rajab, Dhu’l-Qa’dah, Dhu’l-Hijjah and Muharram, these months are called as haraam months – al ashhurul-huroom. In the period of Jahiliyya, there were always civil wars within Arabs. Only haraam months were spent without war. Fairs were set up, poetry contests were held; Jews, Christians and idolatrous people used to spread their religions, in those months. Ramadan is not one of them. The haraam months are mentioned in the Surah At-Tawba in Qur’an Al-Karim:
“Indeed, the number of months with Allah is twelve [lunar] months laid down in Allah’s decree the day He created the heavens and the earth;of these, four are forbidden (haraam). That is the correct religion, so do not wrong yourselves (by breaking the rule) during them. And fight against the polytheists collectively as they fight against you collectively. And know that Allah is with the ones who protect themselves from sins.
Indeed, postponing a haraam month to make war on it is going further in kufr(concealing the truth). Disbelievers are led astray therein. They make it (the haraam month) lawful one year and forbidden another year to violate the number of it which is forbidden by Allah and [thus] make lawful what Allah has forbidden. Made adorned to them is the evil of their deeds; and Allah does not guide the people who conceal the truth.” (At-Tawbah/ The Repentance 9:36-37)