When Yudhishthir asked about the story of suffering of Indra and his wife, Shalya said - "Once Twashtaa, the Swaamee of the creatures, was engaged in severe Tap. In antipathy to Indra, he created a son having three heads. His three heads resembled the Sun, the Moon and the Fire. He read Ved from one mouth, drank wine with another and looked with third as if he will absorb the person into himself. But he was religious and his practices of Tap were very severe.

Afraid of his Tap, lest he takes place of Indra, Indra thought about the way as how to engage him in sensual activities and move him from his Tap. So thinking about it, he ordered his celestial Apsaraa to tempt the son of Twashtaa saying, "Go quickly and engage him in utmost sensual enjoyment. Adorn yourself beautifully and attract him towards yourself." Apsaraa said - "You don't have to fear from his side. We will try our best to control him and end your fears." So as Indra commanded them they went to that three-headed being and started to tempt him with their fine figures and lovely gestures.

But he was like an ocean full to the brim and heavy in gravity. He did see them but did not get influenced by them. Apsaraa got tired so they came back to Indra and spoke - "That being is unapproachable. He could not be tempted by us. You may now act as you want to." Indra respectfully dismissed them and thought to destroy that being with his Vajra (thunderbolt). He threw his Vajra on him, he fell down dead. Although his enemy was dead but still Indra was not at peace, because as he was lying dead, he looked as he was alive. Seeing his valor Indra was thus still afraid.

In the meantime a carpenter came there in that forest with his axe. By chance Indra saw him coming there. So he said to him - "For my sake, cut his heads quickly. Do not fear, at my command your axe will work like a Vajra." Carpenter said - "His shoulders are very thick, I am not sure my axe can cut his heads." Indra said - "Do this quickly, your axe will act like Vajra at my command." At this carpenter asked - "Who are you to give me such orders? May I know this? I want to know the truth." Indra said - "I am Indra. You do the same as I have asked you to do." At this the carpenter said - "Are you not ashamed of your inhuman act? Are you not afraid of killing a Braahman?" Indra said - "I can perform some rigorous religious activities after doing this to purify myself from this sin. This was a very powerful enemy of mine, I have killed him with my Vajra, but I am still afraid of him. Do me this favor, I will give you Var. When people will give sacrifice, they will give you its head as your share. So do it what I have said to you to do."

So the carpenter immediately cut the heads of that dead being. Many birds started coming out of his all heads from where he used to recite Ved and drink Som Ras and look at dreadfully. Now Indra was free from danger, he went back to his Lok and that carpenter had also returned to his home.

When Twashtaa heard of this incident, that Indra had killed his son, he became very furious, he said - "Since Indra has killed my son who was faultless, self-controlled and subdued, I will create Vritra. Let the world and wicked-minded Indra see the power of my Tap." And after saying this he got busy in his sacrifices, made offerings to fire and created a Vritra named Krityaa. He said to him - "Grow in might with the power of my Tap." And he grew in might, and asked Twashtaa - "What should I do for you?" Twashtaa ordered him - "Kill Indra." Vritra proceeded towards Heavens. He caught Indra and in the fight he swallowed Indra.

At this the other Devtaa created Jrimbheek to kill Vritra. As Vritra yawned, Indra came out of his mouth contracting his body, and since then yawn  attached itself to all living beings of three worlds. Devtaa got very happy to see Indra alive. Once again the fight started between them. When Vritra seemed to win, Indra ran away from there. All Devtaa under the leadership of Indra went to see Vishnu and prayed Him. Vishnu said - "You may go to the place where Vritra is there, and Indra, you talk to him about extending friendship. By being invisible I will enter Indra's Vajra (thunderbolt), and thus you will have peace between you and Vritra."

So Devtaa along with Rishi went to Vritra and praising him requested to extend friendship with Indra. Vritra said - "All Rishi are respected for me. First do what I say to you, then I will do my best as Rishi have said. Ask Indra to bestow a Var on me that I should not be killed by any wet or dry, by stone or by wood, by a weapon used in close fights, or by a missile, in day or night. I can make peace only on this agreement." Vritra was given this Var and thus the peace was established. Both Vritra and Indra were satisfied, although latter was still worried about his killing after giving this Var. He was constantly busy in trying to find the way to kill him.

One day, in the evening, Indra saw Vritraasur. Bearing Vishnu in his mind, he took a mass heap of broth of sea and blended with his Vajra threw it on Vritra's face. Vishnu entered that froth and Vritraasur died instantly.

Note
Was it not Namuchi who got this boon from Brahmaa and then was killed by Indra this way? See also 6-38-Balaraam-3.