The day before Diwali is celebrated as Choti Diwali / Narak Chaturdasi.
According to Hindu scriptures, the demon king Narakasura, ruler of Pragjyotishpur (Modern Assam) defeated Lord Indra and snatched away the magnificent earrings of Aditi, the Mother Goddess (the ruler of Suraloka and a relative of Satyabhama, Lord Krishna’s wife) and imprisoned sixteen thousand daughters of the gods and saints in his harem.
Satyabhama appealed to Krishna to kill Narakasura. During the war, Krishna fainted for a while, and an enraged Satyabhama fought and beheaded Narakasura. Krishna returned home in the very early morning of the Narakachaturdashi day. The womenfolk massaged scented oil to his body and gave him a good bath to wash away the filth from his body. Since then the custom of taking bath before sunrise on this day has become a traditional practice specially in Maharashtra.
It is interesting to note that Bhudevi, mother of the slain Narakasura, declared that his death should not be a day of mourning but an occasion to celebrate and rejoice. Since then, Naraka Chaturdasi is being celebrated by people every year with joyous celebrations.In Bengal, Kali, the goddess of Strength, is worshipped on this day and it is known as Kili Chudas.
North Indians call it Naraka Chaudasi and will pray for the souls of departed loved ones.
More details
First Day – Dhanteras
Second Day – Naraka Chaturdasi/Kali Chaudas
Third Day – Diwali
Fourth Day – Vishvakarma Pooja/Govardhan Pooja
Fifth Day – Bhaiya Dooj
The legend of Diwali gambling
Ganesha & Lakshmi mantras for reciting
Ganesha & Lakshmi Stotras for reciting