Imam Rida (a.s) is reported as saying, “If one observes fasting on the last three days of Sha’aban and attach it to the obligatory fasting of Ramadan, Almighty Allah will reward him
as if he has observed fasting for two consecutive months.”
Abu’l-alt al-Harawiy has narrated that when he visited Imam Rida (a.s) on the last Friday of Sha’aban, the Imam said to him, “Abu’lalt: The majority of Sha’aban has passed. This is the last Friday in it. You should thus settle what you have missed in this month by working hard in the rest of it. You may supplicate, seek forgiveness of Almighty Allah, recite the Holy Qur'an, and repent before Almighty Allah from your sins so that you receive the month of Ramadan with pure sincerity to Almighty Allah. You must fulfill all the trusts that you are liable to settle; and do not bear malice against any of your brethren-in-faith; and you must give up any sin that you commit. Fear Almighty Allah and trust in Him in secret and openly, for ‘If any one puts his trust in Allah, sufficient is (Allah) for him. For Allah will surely accomplish his purpose: verily, for all things has Allah appointed a due proportion. 65/3’
In the rest days of Sha’aban, you may repeat the following supplication very much for Almighty Allah saves many people from Hellfire on account of the sanctity of this month:
O Allah: If You have not forgiven us in the past days of Sha’aban,
(Please do) forgive us in the rest of it.
Imam Sadiq (a.s) used to say the following supplication at the last night of Sha’aban and the first night of Ramadhan:
In the name of Allah the Beneficent, the Merciful.
O` Allah! This is the blessed month in which was revealed Quran guidance for men-kind and clear evidence of guidance and discrimination (of the right from the wrong) is being witnessed by us. You therefore keep us healthy in it and keep us sound in our faith in it and accept it from us in a state of prosperity and health granted to us by You.
O` Allah! I ask You to provide me with a way towards all good and keep me away from all that You likes not- O` the Most Merciful!
O` Who forgave me and forgave me all my misdeeds committed secretly.
O` Who punished me not for my disobedience! Your forgiveness. Your forgiveness! Your forgiveness!
O` the Generous! O` my Allah! You did admonish me but I responded not, You did chide but I cared not for it, what excuse have I now?
Pardon me O` the Generous! Your pardon! Your Pardon!
O` Allah! I beseech you for ease at the time of my death and forgiveness at the time of reckoning (on the day of resurrection). Sins of Your slave are great (in number) but forgiveness from You should serve my purpose well. O` the One deserving to be feared and fitted to pardon. Your pardon! Your Pardon!
O` Allah! I am Your bondman son of Your bondman and son of Your slave girl, I am weak and stand in need of Your Mercy. You are Omnipotent and Mighty.
You have reckoned their deeds and accordingly distributed to them their livelihood and made them creation after creation of different languages and colors.
The People know not what You know and esteem You not with the estimation due to You and all of us stand in need of Your mercy- “Turn not You Your face away from us and ordain in Your decree to make me among Your creature virtuous in deeds and hopes.
O` Allah! Keep me alive to live the life of righteousness and cause me to die the best death in a state of love (in my heart) towards Your custodians and in a state of enmity towards Your enemies and with a desire to meet you and fearing You and with humility and fulfilling the promise and submitting to Your will, testifying Your Book and following the life-pattern of Your Messenger.
O` Allah! Remove from my heart any doubt, disbelief, disappointment, in intoxication, conceit insolence, vanity, show, desire from fame, disagreement, hypocrisy, infidels, transgression, disobedience, pride or any thing that You love not.
I therefore ask You to grant me faith (Eeman) according to Your promise and inspire me to fulfill Your promise and pleasure to willingly accept Your decree and piety (ascetics) in the world and a desire of that which is with you (good) impression, mental tranquility and sincere-penitence. I ask You O` Lord! of the Worlds.
O` my Allah! Disobedience to You is due to Your forbearance, and obedience is due to Your generosity and magnanimity as if You were never disobeyed. I and he who never disobeyed are the dwellers of Your earth. You therefore with Your grace pardon me and invite us to You with Your goodness. O` the Most Merciful! And bestow on Mohammad and his progeny Your everlasting and unlimited blessings which neither could be reckoned nor appreciated by any one except You. O` the Most Merciful!
O` Allah! Send Your Blessings on Mohammad and his progeny, Ameen.