From Hindupedia, the Hindu Encyclopedia
The Story of Pundarika
There was once merchant named Pundarika in the town now known as Pandarpur. He was extremely greed and saw his parents as a road block to his prosperity when they became old and infirm and so decided to drive them out of his home. Fortunately for them, they were able to join a group of poor devotees who were going to Varanasi by foot. Later Pundarika himself undertook the pilgrimage to Varanasi but in horse drawn chariot. He crossed his parents on his way, but did not even bother to stop.
After some time, when Pandurika stopped on the bank of a river to rest, he met Rohit Das, a cobbler who had a hermitage by the river bank. Rohit das, though extremely poor, spent all of his time taking care of his parents, even if that meant that he disregard his own comforts. That night, Pandurika saw three ugly women taking bath in the pond of the hermitage and rising up as divine beings. He asked them who they were and they answered that they were the rivers Ganga, Yamuna and Godavari. They had to bear the sins left by people who bathed in them and got cleansed by coming to the Hermitage of Rohit Das.
A sea of change descended on Pundarika. He went back to his parents, begged for forgiveness and from that time onward, spent all his time caring for them. One day Maha Vishnu took the form of a cowherd boy and went to the house of Pundarika. He was told by Pundarika that, he was busy in looking after his parents and did not have time to take proper care of him. Lord Vishnu, informed him, who He was but Pundarika apologized for not being able to receive him as he was too busy taking care of his parents. He gave Lord Vishnu a brick to stand on and asked him to wait there until he was done with his parent's care. Since that day, Lord Vishnu has been standing on that brick. The name of the town is now Pandarpur after Pandurika and the Lord was given the name Vittala or brick since he stands on a brick.
The Story of Rukmini
Once, Queen Rukmini got upset at Lord Krishna (Lord Dwaarkaadisha) and in her anger, left him and went to the Pandharpur Forest. Lord Dwaarkaadish followed her there to supplicate her and also visit his devotee Pundarika.