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, and fight against the Mushrikun (polytheists, pagans, idolaters, disbelievers in the Oneness of Allah) collectively, as they fight against you collectively. But know that Allah is with those who are Al-Muttaqun (the pious) - Surah 9:36
Narrated Abu Bakr (May Allah be pleased with him): The Prophet (ﷺ) said. "(The division of time has turned to its original form which was current when Allah created the Heavens and the Earths. The year is of twelve months, out of which four months are sacred: Three are in succession Dhul-Qa' da, Dhul-Hijja and Muharram, and (the fourth is) Rajab of (the tribe of) Mudar which comes between Jumadi-ath-Thaniyah and Sha'ban."
حَدَّثَنَا مُحَمَّدُ بْنُ الْمُثَنَّى، حَدَّثَنَا عَبْدُ الْوَهَّابِ، حَدَّثَنَا أَيُّوبُ، عَنْ مُحَمَّدِ بْنِ سِيرِينَ، عَنِ ابْنِ أَبِي بَكْرَةَ، عَنْ أَبِي بَكْرَةَ ـ رضى الله عنه ـ عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " الزَّمَانُ قَدِ اسْتَدَارَ كَهَيْئَتِهِ يَوْمَ خَلَقَ السَّمَوَاتِ وَالأَرْضَ، السَّنَةُ اثْنَا عَشَرَ شَهْرًا، مِنْهَا أَرْبَعَةٌ حُرُمٌ، ثَلاَثَةٌ مُتَوَالِيَاتٌ ذُو الْقَعْدَةِ وَذُو الْحِجَّةِ وَالْمُحَرَّمُ، وَرَجَبُ مُضَرَ الَّذِي بَيْنَ جُمَادَى وَشَعْبَانَ ".
Reference : Sahih al-Bukhari 3197; Book 59, Hadith 8; Vol. 4, Book 54, Hadith 419
In another hadith, Abu Bakrah (May Allah be pleased with him) reported: The Prophet (ﷺ) said, "Time has completed its cycle and has come to the state of the day when Allah created the heavens and the earth. The year consists of twelve months of which four are inviolable; three of them consecutive - Dhul-Qa'dah, Dhul-Hijjah and Muharram and Rajab, the month of Mudar (tribe), which comes between Jumada and Sha'ban. What month is this?" We said, "Allah and His Messenger (ﷺ) know better". The Prophet (ﷺ) remained silent for some time until we thought that he would give it a name other than its real name. Then asked, "Is it not (the month of) Dhul-Hijjah?". We replied in the affirmative. He asked, "Which city is this?". We replied: "Allah and His Messenger know better". He remained silent until we thought that he would give it another name. He (ﷺ) asked, "Is it not Al-Baldah (Makkah)?" We said: "Yes". He (ﷺ) asked, "What day is this?". We said: "Allah and His Messenger know better." He (ﷺ) remained silent until we thought that he would give it another name. He asked, "Is it not the day of An-Nahr (the sacrifice)?". We replied in the affirmative. Thereupon he said, "Your blood, your property and your honour are inviolable to you all like the inviolablity of this day of yours, in this city of yours and in this month of yours. You will soon meet your Rubb and He will ask you about your deeds. So do not turn to disbelief after me by striking the necks of one another. Behold! Let him who is present here convey (this message ) to him who is absent; for many a person to whom a message is conveyed has more retentive memory than the one who hears it." He (ﷺ) again said, "Have I conveyed the message to you? Behold! Have I conveyed the Commandments (of Allah) to you." We submitted: "Yes". He then said, "O Allah, bear witness (to this)".
Reference : Al-Bukhari and Muslim; Riyad as-Salihin 213
Rajab, the 7th month of the lunar year, stands apart from the other sacred months. It is thus called ‘Rajab al-Fard’ or ‘Rajab the Separate One’.
Some scholars have mentioned that ‘Rajab’ is composed of three letters, which represent other profound words:
Ra - for Rahmah: representing the Rahmatu-Allah, the mercy of Allah
Jeem - for Juud: representing Juudu-Allah, the generosity of Allah
Ba - for Birr: representing Birru-Allah, the kindness of Allah
Virtues of Rajab month:
1. Month of Allah: The Prophet (saw) said, ‘Rajab is the month of Allah, Sha‘ban is my month and Ramadan is the month of my Ummah’. [Suyuti]
2. Historic and momentous events:
The marriage of the noble parents of the Prophet (saw)
Aminah, the noble mother of the Prophet (saw) becoming pregnant with the Best of Creation (saw)
The miraculous Night Journey & Ascension (Al-Isra’ wal-Mi’raj), which took place on the 27th night of Rajab, according to the dominant opinion.
We received three divine gifts during Al-Isra’ wal-Mi’raj:
The gift of our five daily prayers, which ground our days in the worship of Allah
The last two ayat of Surah Baqarah, of which the Prophet (saw) said, ‘Whoever recites the last two verses of Surah Baqarah in the night, it will suffice him’. [Bukhari]
Allah’s gift to the believers: Whoever dies believing in Allah and not associating anything with Him, will enter Paradise. [Nasa’i]
3. ‘Rajab al-Asabb’ or ‘the Pouring Rajab’ - because Allah pours His numerous blessings and favours down during this month, as well as His abundant mercy.
4. Month of Tawbah (repentance) and the Month of Istighfar (seeking forgiveness).
Most Muslims - increase their good deeds and worship during Ramadan, hoping to receive the blessings and mercy which are pouring down. But we also have a chance to do this during Rajab, remember, our deeds weigh heavier on the scales in the sacred months, so this is an excellent opportunity to invest in our akhirah.
5. Rajab is also called as 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. This was the postponing referred to in the ayah:
اِنَّمَا النَّسِىۡٓءُ زِيَادَةٌ فِى الۡكُفۡرِ يُضَلُّ بِهِ الَّذِيۡنَ كَفَرُوۡا يُحِلُّوۡنَهٗ عَامًا وَّيُحَرِّمُوۡنَهٗ عَامًا لِّيُوَاطِـُٔـوۡا عِدَّةَ مَا حَرَّمَ اللّٰهُ فَيُحِلُّوۡا مَا حَرَّمَ اللّٰهُ ؕ زُيِّنَ لَهُمۡ سُوۡۤءُ اَعۡمَالِهِمۡ ؕ وَاللّٰهُ لَا يَهۡدِى الۡقَوۡمَ الۡـكٰفِرِيۡنَ
“The postponing (of a Sacred Month) is indeed an addition to disbelief: thereby the disbelievers are led astray, for they make it lawful one year and forbid it another year in order to adjust the number of months forbidden by Allah, and make such forbidden ones lawful.” [Surah Al-Tawbah 9:37]
To further emphasise its sanctity, Rajab is also called -
6. ’Rajab al-Murajjab’, which means that it is extraordinarily honoured, revered and magnified.
7. ‘Rajab al-Asamm’, which means ‘the Deafening and Silent Rajab’. This is because you cannot hear the clashing of swords during Rajab, as fighting is prohibited.
Tips to Help You Benefit From This Month:
1. Think about your intention.
2. Seek forgiveness, and forgive!
3. Fast some extra days.
4. Strengthen your body & deprive yourself.
5. Literally, keep your tongue moist with dhikr.
6. Ask for Taufeeq (ability).
Rest Allah knows best.
Source: Quran, Sunnah.com, https://muslimhands.org.uk/, IslamQA