Once the mighty priest Tvashtri, out of dislike for the god Indra, created a three-headed son to take over Indra's throne. This son was a pious ascetic who appeared to be mastering the universe with his three heads, which made Indra uneasy. After futilely tempting Tvashtri's son with dancing girls, Indra slew the radiant young man with a thunderbolt and ordered that his three heads be cut off.
Enraged, Tvashtri made a colossal dragon named Vritra to destroy Indra. This serpent reached up to the heavens and swallowed Indra. But Indra tickled its throat and leapt out to resume battle. The dragon proved too strong and Indra had to flee. At length he went to the god Vishnu, who advised him to compromise with the dragon. The serpent agreed to peace, provided that Indra did not attack it with solid or liquid, or attack it by day or night. Indra, however, nursed his resentment and tried to get around this agreement.
One evening at twilight Indra saw a huge column of foam containing the god Vishnu, so he hurled this at the dragon, who fell dead. The gods and men rejoiced at the serpent's death, but Indra bore a great sin for killing a priest's son.