One verse

Srimad Bhagavatam 10.1.10

10.1.10

व्रजे वसन् किमकरोन्मधुपुर्यां च केशव: । भ्रातरं चावधीत् कंसं मातुरद्धातदर्हणम् ॥ १० ॥

vraje vasan kim akaron madhupuryāṁ ca keśavaḥ bhrātaraṁ cāvadhīt kaṁsaṁ mātur addhātad-arhaṇam

vraje
at Vṛndāvana
vasan
while residing
kim akarot
what did He do
madhupuryām
in Mathurā
ca
and
keśavaḥ
Kṛṣṇa, the killer of Keśī
bhrātaram
the brother
ca
and
avadhīt
killed
kaṁsam
Kaṁsa
mātuḥ
of His mother
addhā
directly
a-tat-arhaṇam
which was not at all sanctioned by the śāstras.

Lord Kṛṣṇa lived both in Vṛndāvana and in Mathurā. What did He do there? Why did He kill Kaṁsa, His mother’s brother? Such killing is not at all sanctioned in the śāstras.