Vishwaamitra Jee was doing severe Tap to become Brahmarshi, and Vashishth Jee was not declaring him Brahmarshi. So Vishwaamitra Jee thought that it was Vashishth Jee who did not want him to become Brahmarshi. So he started towards Vashishth Jee's Kutee to ask as why he did not want him to become Brahmarshi. When he arrived there, he overheard Arundhatee asking her husband, "Why don't you declare Vishwaamitra Jee Brahmarshi?"  He said, "It is not easy, because his "I" (ego) must die, then only he can become Brahmarshi; besides he has to be very calm and patient and should never lose his temper. He does not follow this so what use of his Tap is?"  Now Vishwaamitra Jee interpreted that in this way that "unless Vashishth will die I cannot be Brahmarshi so he entered Vashishth Jee's Kutee with the intention to kill him. Vashshth Jee said, "See, what I was saying to you. He is so angry that he is not trying to follow the things. His "I" (Aham, or ego) is not yet gone." Then he understood what he wanted to say.

Raajaa Dileep was childless, so he came to Vashishth Jee and asked the reason. He told that once you passed by Kaamdhenu cow without greeting her that is why you don't have a child. Then he told if you serve her (Kaamdhenu's) daughter Nandinee, then you can get a child. 

Raajaa Raghu was married to Indumatee. They had a son named Aj. Indumatee died young, and king forgot his royal duties in her sorrow. Vashishth Jee said - "Birth and death are not in our control. You may die in her sorrow, but still you will not get her back. Storms come but mountains do not move, you should be like a  mountain."

This Kathaa comes in Skand Puraan's Naagar Khand. Once there was a very mighty king named Satyavrat (popularly known as Trishanku after this event) in Soorya Vansh (lineage). Brahmaa Jee appointed Vashishth Jee as Purohit of Soorya Vansh. Satyavrat was so much proud of his might that he thought he could go to Swarg with his mortal  body. So he went to Vashishth Jee and expressed his wish and asked the way. Vashishth Jee said - "There is no way one can go there with this body." 

Trishanku didn't like it, so he gave a thought to try Vashishth's 100 sons. But they also agreed with their father. Trishanku got disappointed as well as furious and told that he would appoint any other Rishi to do that Yagya and they lacked required knowledge to perform such a Yagya. At this Vashishth's sons gave him Shaap - "Be a Chaandaal (a low caste)." The next moment he became a Chaandaal. Now he was so much ashamed of himself that he went to the forest. He handed over his kingdom to his son Harishchandra.

One day while wandering in the forest, Trishanku met Sage Vishwaamitra Jee. He narrated his plight to him too. Since Vishwaamitra was the competitor of Vashishth Jee, he got an opportunity to prove his superiority over Vashishth Jee. He told him that he could send him to Swarg with this mortal body. But he had to go for a pilgrimage to become pure before that. So both set out for the pilgrimage.

On their way to the piligrimage, at Arbudaachal, they met Muni Maarkandeya. Vishwaamitra Jee told him everything in detail and said - "I have taken the vow to free Trishanku from Vashishth's sons' Shaap, but I have not succeeded yet, so I have renounced the world. Maarkandeya Muni consoled him and instructed him to go to Haatkeshwar where taking a dip in Paataal Gangaa will purify Trishanku. Trishanku did so and he was surprised to see that all the qualities of a Chaandaal had vanished from him and he was purified. Vishwaamitra Jee was also very happy to see this.

Then Vishwaamitra Jee went to Brahm Lok to request Brahmaa Jee to be present at the Yagya to send Trishanku to Swarg with his mortal body, and asked Trishanku to make necessary preparations for the Yagya. Brahmaa Jee said "Although it was impossible to go Swarg with the mortal boy but if you will complete all rituals diligently then he could go there." Vishwaamitra didn't like His comments and he challenged Him that no power could stop him sending him there.

So they started Yagya. It continued for 12 long years but there was no sign to go to Swarg. Trishanku got dejected and intended to go to forest for Tap. He could not go to his kingdom because he was afraid that Vashishth's sons would make fun of him. But Vishwaamitra Jee consoled him that he would surely send him to Swarg, he should just wait. Then he worshipped Shiv Jee. Shiv Jee got pleased and granted him the desired Var. Vishwaamitra asked Him to bestow the powers to create universe like Brahmaa. Shiv Jee did so and disappeared.

Now Vishwaamitra was eager to test those powers. He did so and created everything from stars etc to sky, river mountains etc. Soon the place was filled with his creation resulting chaos all over. Now everything were two, one was created by Brahmaa and the other one created by Vishwaamitra. This created a fallout of natural course of events.

Everybody requested Brahmaa Jee to bring an order in the universe. Brahmaa Jee asked Vishwaamitra to stop his creation. He replied that he could do it if He will allow Trishanku to go to Swarg with his mortal body. At last Brahmaa Jee allowed him to go to Swarg.

Ikshwaaku (Manu's son born from his sneeze) had three sons, Vikukshi, Nimi, and Dand. Once Nimi wanted to do a Yagya, so he requested Vashishth Jee to be his Hotaa. Vashishth Jee said, "At present I am going to do Indra's Yagya, but I will come back soon, so wait for me." And he went away. Nimi thought  "Life is too short" so he appointed another Hotaa till Vashishth Jee came. 

When Vashishth Jee came back from Indra's Yagya, he came to know that Raajaa Nimi had appointed another Hotaa, then he gave Shaap to him, "You are very proud of your knowledge and thoughtfulness, so your body should fall down." His Shaap was not according to Dharm, so Raajaa Nimi also gave Shaap to him, "You also did not respect Dharm because of your greed, so your body should  also fall down." After saying this Nimi left his body through Yog, and Vashishth Jee also left his body. He was reincarnated as the son of Mitraavarun and Urvashee. And the same Vashishth was the Purohit of Soorya Vansh in Raam's times.