Imam Ja`far al-Sadiq (as) has reported the Holy Prophet (saws) as saying: Rajab is the month of imploring for forgiveness for my people; so, you should implore forgiveness repeatedly in this month much more than you do in other months, for Almighty Allah is forgiving and merciful. This month is described as the advantageous month, because mercy is poured on my people during it so heavily. You should thus repeat very much the following imploration prayer
أَسْتَغْفِرُ اللّه وَأَسْأَلُهُ التّوْبَة
astaghfiru allaha wa as'aluhu alttawbata
I ask Allah for forgiveness and I pray Him to accept my repentance.
It is recommended to fast on three days in the month of Rajab: Thursday, Friday, and Saturday. It has been narrated that one who fasts on these three days in one of the Sacred Months will be awarded with the reward of nine hundred year worship.
If one is incapable of fasting during the month recite the following instead 100 times each day in the month of Rajab:
سُبْحَانَ الإِلٰهِ ٱلْجَلِيلِ
subhana al-ilahi aljalili
سُبْحَانَ مَنْ لا يَنْبَغِي ٱلتَّسْبِيحُ إِلاَّ لَهُ
Glory be to the All-majestic God.
subhana man la yanbaghi alttasbihu illa lahu
سُبْحَانَ ٱلاعَزِّ ٱلاكْرَمِ
Glory be to Him other than Whom none should be glorified.
subhana al-a`azzi al-akrami
سُبْحَانَ مَنْ لَبِسَ ٱلْعِزَّ وَهُوَ لَهُ اهْلٌ
Glory be to the All-honorable and All-dignified.
subhana man labisa al`izza wa huwa lahu ahlun
Glory be to Him Who has dressed Himself with grandeur that fits none but Him.
The Holy Prophet (saws) is reported as saying: Whoever repeats the following imploration for forgiveness 100 times in Rajab and immediately gives alms after it, Almighty Allah will conclude his life with mercy and forgiveness. Also, whoever repeats it 400 times, will be given the reward of one hundred martyrs:
اسْتَغْفِرُ ٱللَّهَ ٱلَّذِي لاَ إِلٰهَ إِلاَّ هُوَ
Astaghfirullaha alladhy la ilaha illa huwa
I implore the forgiveness of Allah. There is no god save Him,
وَحْدَهُ لا شَرِيكَ لَهُ
the One and Only Who has no partner,
wa atubu ilayhi.
and I repent before Him.
The Holy Prophet (saws) is also reported to have said: Whoever repeats this litany 1000 times in Rajab, Almighty Allah will decide for him 100,000 rewards and award him 100 houses in Paradise:
لاَ إِلٰهَ إِلاَّ ٱللَّهُ
La ilaha illa allah
There is no god save Allah.
A Hadithh reads that whoever repeats the following imploration for forgiveness 70 times in the morning and 70 times in the evening on each day in Rajab, will be admitted by Almighty Allah if he dies in Rajab and Hellfire will not touch him on account of the blessings of Rajab:
اسْتَغْفِرُ ٱللَّهَ وَاتُوبُ إِلَيْهِ
Astaghfirullaha wa atubu ilayhi
I implore the forgiveness of Allah and I repent to Him.
After this repeat seventy times, raise the hands towards the sky and say:
اَللَّهُمَّ ٱغْفِرْ لِي وَتُبْ عَلَيَّ
allahuma aghfir li wa tub'alayya
O Allah, (please do) forgive me and accept my repentance.
It is recommended to implore Almighty Allah for forgiveness in the following form one thousand times in Rajab so that He will forgive:
اسْتَغْفِرُ ٱللَّهَ ذَاَ ٱلْجَلاَلِ وَٱلإِكْرَامِ
Astaghfiru allaha dhaljalali wal ikrami
I implore Allah, the Lord of majesty and honor,
مِنْ جَمِيعِ ٱلذُّنُوبِ وَٱلآثَامِ
min jami i aldhunubi wa ithmi
to forgive my all sins and offenses.
One who recites Surah Tawheed 100 times on Fridays in Rajab will enjoy, on the Resurrection Day, light that draws him towards Paradise.
It has been narrated that the Holy Prophet (saws) said, “One who recites Surah al-Tawheed 100 times at one night in Rajab will be decided to have fasted for one hundred years for the sake of Almighty Allah Who will also decide for him one hundred palaces (in Paradise) in the vicinity of one of the Prophets.”
The Holy Prophet (saws) is also reported as saying that Almighty Allah will forgive all the sins of those who offer a ten unit prayer, at one night in Rajab, reciting in each unit Surah al-Fatihah once and repeating Surah al-Tawheed three times.