Budhashtami Vrat Katha or the Story of Budh Ashtami vrat is mentioned in the Bhavishya Purana. Budhashtami is observed on the Ashtami tithi which falls on Budhwar, Wednesday.
Budhashtami Vrat katha goes like this…
There used to be a brahmana named Dhira whose wife was named Rambha. Dhira’s son was Koushika, his daughter was Vijaya and Dhira’s bull was named Dhanada. Koushika would go with the other cowherds to graze the bull. Once when Koushika was having a bath in the river Bhagirathi and the bull was grazing, some thieves came and stole the bull. Koushika and his sister Vijaya looked everywhere for it, but could not find it.
In searching for the bull, they came to lake where some women were bathing in the course of performing a vrata. Brother and sister were tired and hungry and they craved for some food. The women agreed to give them food, but only after Koushika and Vijaya had also performed the budhashtami vrata. And as soon as Koushika performed the ritual, the bull was miraculously returned to him. Such were the powers of the vrata that Koushika could get his sister Vijaya married off to Yama and himself became the king of Ayodhya.
After their parents Dhira and Rambha had died. Vijaya discovered that her father and mother were in naraka. When she asked Yama as to how her parents might be delivered from naraka, Yama told her that Koushika and Vijaya should perform budhashtami vrata again. And immediately after they did so, the parents attained svarga.