Abu Bakrah relates that the Prophet ﷺ gave his Farewell Sermon and said: “Time has completed its cycle and is as it was on the Day when Allah created the heavens and the earth. The year is twelve months, of which four are sacred, three consecutive months – Dhoo’l-Qa’dah, Dhoo’l-Hijjah and Muharram – and the Rajab of Mudar which comes between Jumaada and Sha’baan.”
(Bukhari and Muslim)
Rajab, the seventh month of the lunar calendar, is among the four sacred months in Islam. It was called Rajab of Mudar because (the tribe of) Mudar did not tamper with its timing, unlike the rest of the Arabs, who used to tamper with the months and change their order depending on whether they were in a state of war or not. Besides Al Mudar, Rajab is called by many other unique names, some of which are Al Mutahir (the chemical), Al Muali (the lift), Al-Murajjab (extraordinarily honoured, revered and magnified), and Al-Asamm (the Deafening and Silent because fighting is prohibited therein).
Rajab is the month when Prophet Muhammad ﷺ travelled from the holy Ka’abah in Makkah to Al-Aqsa in Jerusalem and finally ascended to heaven with Angel Gabriel. Therefore, performing good deeds such as praying, self-introspection and seeking forgiveness from Allah are highly rewarding things to do.
Prophet Muhammad ﷺ asked his followers to recite, Allahumma barik lana fi Rajaba wa Sha’bana wa ballighna Ramadana, on the sighting of Rajab moon. (O Allah! Make the months of Rajab and Sha’ban blessed for us and let us reach the month of Ramadan.)