One verse

Srimad Bhagavatam 10.1.68

10.1.68

आत्मानमिह सञ्जातं जानन्प्राग् विष्णुना हतम् । महासुरं कालनेमिं यदुभि: स व्यरुध्यत ॥ ६८ ॥

ātmānam iha sañjātaṁ jānan prāg viṣṇunā hatam mahāsuraṁ kālanemiṁ yadubhiḥ sa vyarudhyata

ātmānam
personally
iha
in this world
sañjātam
born again
jānan
understanding well
prāk
previously, before this birth
viṣṇunā
by Lord Viṣṇu
hatam
was killed
mahā-asuram
a great demon
kālanemim
by the name Kālanemi
yadubhiḥ
with the members of the Yadu dynasty
saḥ
he (Kaṁsa)
vyarudhyata
acted inimically

In his previous birth, Kaṁsa had been a great demon named Kālanemi and been killed by Viṣṇu. Upon learning this information from Nārada, Kaṁsa became envious of everyone connected with the Yadu dynasty.