According to the Vishnu Purana, Goddess Lakshmi was born as the daughter of Bhrigu and resided in Swarg, but due to the curse of Rishi Durvasa, she left Swarg and took refuge in Ksheersagar or the ocean of milk.
The story related to the relation of Lord Vishnu and Goddess Lakshmi is as follows. The story begins with Indra devta, the lord of Devtas, who had become arrogant in his ways. He had a very elegant elephant named as Aviratha. One fine day, Lord Indra went to the jungles, where he met Rishi Durvasa. Rishi Durvasa was famous for his short temper and had maintained a long list of cursing devtas who were reduced to nothing because of his curses.
When Indra met Rishi Durvasa, Durvasa gave him his garland as a sign of respect for the lord of devtas. Lord Indra unwittingly put the garland across the neck of his elephant Aviratha, which got irritated due to the fragrance of the garlands and hence threw them to the ground and stepped on it.
Rishi Durvasa got enraged by this disrespect and there occured a futile argument between Indra and Durvasa. Rishi Durvasa, cursed Indra that soon, he and his devtas with lose all their powers and will be reduced to nothing.
Taking advantage of the situation where Devtas were weakened by Rishi Durvasa’s curse, demons attacked the heavens and drove all the devtas out of the heavens.
Helpless Devtas, went to Lord Brahma, the God of creation, to make them immortal by churning the Ocean of milk, the Ksheersagar. Lord Brahma required the help of Lord Vishnu in order to carry out the enormous task. For help, the devtas visited Lord Vishnu who went down to earth to help the devtas and maintain the balance of good and evil in the universe.
Lord Vishnu along with the help of Vasuki, the lord of Serpents, started churning the ocean of milk, Vasuki himself being the stick with which the ocean was churned.
Out of the Ocean, came Goddess Lakshmi who immediately defeated and killed all the demons who had captured the heavens. She then married Lord Vishnu, the one and only who could control Maya, the illusion. For this reason Lakshmi is also called the daughter of the sea. From the Ocean, also came out the moon, which is also known as her brother.