Kumail bin Ziyaad al-Nakha ii (RA) relates:
One day I was seated before my aqa Amirul Mumineen (AS), with us were his as-haab - we were gathered in the masjid of Basara. Somone asked, "O' Mola! What is the meaning of, "Feeha yufraqo kullo amrin hakeem"? (Quranic aayat, "In it every decreed matter is made separate"). And in which way?"

Molana Ali said in response: "That night is the eve of the middle of Shabaan, the 15th eve of Shabaan." Amilrul Mumineen continued, "Upon the oath of Allah in whose hands is my soul, for every subject (person) good and bad is written - when is it written? On the middle eve of Shabaan; beginning from there and until the year's end it goes on being written until the same eve comes around the following year."

"Upon Allah's oath, no individual will not spend it in worship and recite the dua of Khidr (a.s.) but that Allah will hear his prayer."

"Everyone left then", Kumail says, "That night I went to Amirul Mumineen's house and knocked on the door. From inside the house came the words, "O' Kumail! So long into the night, at this late time, why have you come?" I submitted, "You spoke of the dua mubarak of Khidr (a.s.), which dua is that?"

Molana Ali replied, "O' Kumail, be seated, memorize this dua. On every eve of Jumoa or once every year or once in a lifetime whosoever recites this dua Allah taala will accommodate for their needs, will assist them, provide for them and they will never forgo forgiveness."

"O' Kumail. Your long companionship compels me to give to you what you ask." Molana Ali continued, "Kumail, write it down" and proceeded to have the dua written down in its entirety.

In the era of the A'immat Fatemiyyeen (a.s.) - in al-Moizziyatul Qahera (Cairo) - the masjids and other places of gathering would be decorated on four nights in the year including the first and fifteenth eves of Shabaanal Kareem.