Srimad Bhagavatam Canto 07, Chapter 01, Text 20

SB 7.1.20

katham tasmin bhagavati
 duravagrahya-dhamani
pasyatam sarva-lokanam
 layam iyatur añjasa
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
How was it possible for Sisupala and Dantavakra, in the presence of many exalted persons, to enter very easily into the body of Krsna, whose nature is difficult to attain?
 
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
Sisupala and Dantavakra were formerly Jaya and Vijaya, the doorkeepers of Vaikuntha. Merging into the body of Krsna was not their final destination. For some time they remained merged, and later they received the liberations of sarupya and salokya, living on the same planet as the Lord in the same bodily form. The sastras give evidence that if one blasphemes the Supreme Lord, his punishment is to remain in hellish life for many millions of years more than one suffers by killing many brahmanas. Sisupala, however, instead of entering hellish life, immediately and very easily received sayujya-mukti. That such a privilege had been offered to Sisupala was not merely a story. Everyone saw it happen; there was no scarcity of evidence. How did it happen? Maharaja Yudhisthira was very much surprised.
Srimad Bhagavatam Canto 07, Chapter 01, Text 19
Srimad Bhagavatam Canto 07, Chapter 01, Text 21