Towards the south of the country there was a mountain named Brahmaparvata. There the sage Goutama and his wife Ahalya performed tapasya for ten tousand years. While they were meditating, there were no rains in the forest for a hundred years and there was a shortage of water. Living beings died from the drought. Goutama prayed to Varuna, the god of the ocean and the rain. Varuna appeared and offered to grant a boon.
Please grant the boon that it might rain, said Goutama.
I can't do that, replied Varuna. That is beyond my powers. Ask for something else instead.
Then let us have a pond in the forest that will always be full of water, said Goutama.
This was within Varuna's powers and the pond was created. The other sages also began to use water from this pond. Normally, Goutama sent his disciples to fetch water. But the disciples complained that the wives of the other sages did not let them take the water. So Ahalya herself started to fetch the water. The wives of the other sages annoyed and pestered Ahyalya, but she never reacted. These wives then complained to their husbands about Ahalya and Goutama. At first the sages did not listen, but eventually, they were convinced that Ahalya and Goutama were wicked. They therefore sought to devise a plan so that these two might punished. They began to pray to Ganesha.
When Ganesha arrived, the sages said, Please grant us the boon that Goutama and Ahalya might be banished from the hermitage.
Although Ganesha realized that this was an unfair boon, he decided to grant it because he realized that the sages and their evil wives needed to be punished.
Goutama had some fields of paddy and grain. Ganesha adopted the form of a lean and starving cow and began to eat up the crop. Goutama tried to drive away the cow with a blade of grass. But as soon as he struck the cow with the blade of grass, the cow fell down and died. This was a terrible calamity.
It was the killing of a cow.
The other sages banished Goutama and Ahalya from the hermitage. They had to set up an ashrama (hermitage) that was a fair distance away. The other sages completely disassociated themselves from Goutama and Ahalya. Goutama began to think of ways of performing prayashchitta (penance) for the crime that he had committed. The other sages told him that he would first have to travel around the world. After that, he would have to pray very hard for an entire month. The next task was to circle Brahmaparvata a hundred times and bathe in a hundred pots of water. This would complete the penance.
All this Goutama and Ahalya did. They also prayed for a long time to Shiva.
Shiva appeared before them and offered them a boon. Goutama desired the boon that the river Ganga might always be present in the hermitage. Ganga said that she would agree subject to the condition that Shiva and Parvati were also always present in the hermitage. Parvati and Shiva agreed to do this. This established Trymbaka, the eighth of the jyotirlingas. The river Ganga which flowed there came to be known as the Godavari. So Trymbaka is on the banks of the Godavari.
What happened to the evil sages and their wives? Goutama asked that they might be pardoned. They performed penance by circling Brahmaparvata one hundred and one times, and begged forgiveness from Goutama and Ahalya.