Srimad Bhagavatam Canto 10, Chapter 36, Text 20

SB 10.36.20

pratiyate tu devarsau
 kamsa abhasya kesinam
presayam asa hanyetam
 bhavata rama-kesavau
 
Translation: 
 
After Narada left, King Kamsa summoned Kesi and ordered him, “Go kill Rama and Krsna.”
 
Purport: 
 
Before having Krsna and Balarama brought to Mathura, Kamsa tried sending one more demon to Vrndavana.
Srimad Bhagavatam Canto 10, Chapter 36, Text 19
Srimad Bhagavatam Canto 10, Chapter 36, Text 21