The Four Sages
The four Kumaras — Sanaka, Sanandana, Sanatana, and Sanatkumara — were the mind-born sons of Brahma. They were eternally young, perpetually five years old in appearance, and among the greatest sages of the universe.
They came to Vaikuntha to visit Vishnu.
Jaya and Vijaya, the divine gatekeepers, stopped them. The Kumaras, they said, could not enter now — the Lord was resting.
The Curse
The four sages were not accustomed to being turned away from anywhere, least of all from the abode of the Lord they wished to visit. Their anger, though righteous, resulted in a curse:
"Since you have used your position to obstruct those who seek the Lord, you shall be deprived of Vaikuntha and born in the mortal world — as enemies of the Lord himself."
Vishnu's Response
Vishnu heard the commotion and came to the gate himself. He apologized to the sages for his doorkeepers' action and invited them in.
Then he turned to Jaya and Vijaya. He could have countered the curse. Instead, he said:
"This curse must stand. But you have a choice: be born seven times on earth as my devotees — in which case you will return to Vaikuntha after seven lives — or be born three times as my enemies, and return in three. Which do you choose?"
Jaya and Vijaya, unable to bear seven lives apart from their Lord, chose three. They were born as Hiranyakashipu and Hiranyaksha, then as Ravana and Kumbhakarna, then as Shishupala and Dantavakra.
In each life, Vishnu himself incarnated to defeat them and free them. In each death at the Lord's hands, they returned a step closer to Vaikuntha.