The story the relation of Rishi Vishwamitr being related to Parashuram, the sixth incarnation of Bhagwan Vishnu is a less known but an interesting one.
There was once a king named a righteous king Gaadhi who ruled over the kingdom of Kanyakubja. Gaadhi had a beautiful daughter named Satyavathi. Once Sage Ruchika who was Rishi Chavany’s son came to the kingdom of Kanyakubja and saw Satyavathi. He was mesmerised with her beauty and decided to marry her and expressed his desire to Gaadhi. Although Gaadhi is surprised, but Satyavathi agrees to the proposal keeping in view the righteousness of her father and gets married to Rishi Ruchika.
Satyavathi was very devoted to her husband and did all her duties with great servitude to her husband. However she was unhappy that her father had no other children who would inherit his throne. Rishi Ruchika comes to know about this and gives two bowls of sweet porridge to Sathyavathi. He then mentions that one bowl had the power to give a son who would be a great warrior and the other to give a great Sage. He then tells Satyavathi to give the first bowl to her mother and take the second bowl for herself. Pleased with this, Satyavathi goes to her mother and mentions the same and gives her the bowl which would give her a great warrior.
But Satyavathi’s mother doubts the intention of Satyavathi that why her daughter would wish for a sage and drinks the porridge meant for Satyavathi. Not knowing this, Satyavathi consumes the other bowl and returns back. A few days later, Rishi Ruchika comes to know that Satyavathi is pregnant, but surprised to see the aura of a warrior coming out of her womb. With his divine sight, he comes to know of what has happened and mentions the same to Satyavathi.
Satyhavathi feels sad for what has happened and laments that she does not wish for a warrior but a divine sage like her husband. However, as it was impossible to change what has happened, Rishi Ruchika prophesizes that although their son would have warrior abilities, his power would be transferred to the next generation. In the same way, Satyavathi’s mother would give birth to a son who would be a warrior , but later on go to become one of the greatest sages mankind has ever known.
Sathyavathi gives birth to Kaushik, who later on went to be a great king. But when he encountered Rishi Vashisht, he came to know the power of penance and renounced his life as a king and went on to become the great Brahmarshi Vishwamitr. Meanwhile, Satyavathi gave birth to Rishi Jamadagni who was a sage, yet was famed as a sage who was an expert in the art of weaponry.
As prophesized by Rishi Ruchika, Jamadagni’s warrior abilities were shifted to his son Parashuram, the incarnation of Bhagwan Vishnu who was known for his fighting prowess in the world. Later Rishi Viswamitr went to become the preceptor of Shri Ram. Parashuram too had an encounter with Shri Ram which gave him the realisation that the seventh incarnation of Bhagwan Vishnu had arrived to protect Dharma. While Rishi Vishwamitr gave all his knowledge of weaponry to Shri Ram, Parashuram passed his divine soul of Bhagwan Vishnu to Shri Ram. Thus, were the two great personalities related to each other and were also the important personalities who pathed the way of Shri Ram in the welfare of Dharma.