Kalmashpada's son

When Kalmashpada was living his life as a rakshasha, he roamed around the land looking for humans to eat. One day he saw a brahmana couple. Wanting to eat them, he grabbed the brahmana. The brahamana lady started pleading with the Rakshasha. She said, I know you are Kalmashpada, son of Soudasa. Please leave my husband. I want to conceive a child through him. If you really want to eat, eat me instead of my husband.

The king, under the spell of the rakshasha, did not listen and killed the brahmana.
The dead brahmana's wife then collected wood from the forest and lit a pyre. Collecting the remains of her husband, she cursed Kalmashpada, saying if he ever touched a woman, he would die. His clan would be carried forth through Vashishtha, whose son you killed. Saying this, she jumped into the pyre.

Years later, Kalmashpada was relieved from the rakshasha. He went back to his kingdom and led a pious life. Not having any children and wishing for a child, he went to his wife, Madayanti.

Madayanti knew about the curse and she told the king, the moment he touched her, he would die. He went to Vashishtha with his wife, and asked the sage to help beget a child.
 Thus Vashistha saved the clan from getting destroyed.

Kalmashpada

Vishwamitra kept looking for ways to get back at Vashishtha. He found his excuse in the king called Kalmashpada, son of Saudasa. Kalmashpada was born in the Ikshvaku dynasty. Vashishtha was his priest.
One day the king, holding a sacrifice, invited Vashistha. Being busy, the sage refised. Angry, the king decided to call Vishwamitra. He went to invite Vishwamitra and on his way back along with Vishwamitra, they came across Shakti, son of Vashishtha.
As the path was narrow, the king asked Shakto to give way. Shakti said, as a brahman, he needed to go first. The king said he ruled the land and he had right to the path.
Both started quarelling, none of them willing to give way. The king angry, struck Shakti with a whip. Shakti started bleeding.
Angry Shakti cursed the king. He said Though born in a high dynasty, your behavior is not like that of one. I curse you to become a cannibal.
The king started pleading with Shakti.
Vishwamitra, who had been watching this invoked the spirit of a cannibal and installed it in the king. Possessed, the king killed Shakti and ate him up.
Having eaten up Shakti, he became terrible in form.
Vishwamitra took the king now to the place where Vashistha's hundred sons were. Seeing the sons, the king ate then up also.
Vashishtha was not there at that time. When he came home, he saw an empty house.
Meditating, he realized that Vishwamitra was the cause of all this.
Saddened, he wanted to kill himself.
He immersed himself in the ocean to drown himself. He was unable to drown. He then came out and went to the mountains and jumped from a high peak, but he did not die.
He then lit a fire and jumped inside that. The fire died down as soon as he entered. He entered a dense forest hoping that the wild beasts would eat him; even that did not happen.

Dejected, he came home and seeing an empty house he was sad. He wanted to kill himself again. He saw a flowing river full of crocodiles. He was about to jump in, when he heard the sound of Vedas and also someone calling him. Turning, he saw Shakti's wife. He asked her who was reciting the Vedas. The woman said, it was her unborn child.

Happy that his dynasty had not ended, Vashishtha took Shakti's wife along, and brought her home.
One day Vashistha came across the king, Kalmashpada who was living,  eating human flesh. Seeing the sage, the king rushed to eat him. Vashishtha sprinkled some water from the pot he was carrying. The spirit that had possessed the king left, and the king was back to normal.

Regaining consciousness, the king fell at Vashishtha's feet and begged for forgiveness.

The sage forgave him and the king left.