Srimad Bhagavatam Canto 10, Chapter 16, Text 33

SB 10.16.33

naga-patnya ucuh
nyayyo hi dandah krta-kilbise ’smims
tavavatarah khala-nigrahaya
ripoh sutanam api tulya-drstir
dhatse damam phalam evanusamsan
 
Translation: 
 
The wives of the Kaliya serpent said: The punishment this offender has been subjected to is certainly just. After all, You have incarnated within this world to curb down envious and cruel persons. You are so impartial that You look equally upon Your enemies and Your own sons, for when You impose a punishment on a living being You know it to be for his ultimate benefit.
Srimad Bhagavatam Canto 10, Chapter 16, Text 32
Srimad Bhagavatam Canto 10, Chapter 16, Text 34