Srimad-Bhagavatam: Canto 10 - Chapter 1 - Verse 10


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


vraje vasan kim akaronmadhupuryāṁ ca keśavaḥbhrātaraṁ cāvadhīt kaṁsaṁmātur addhātad-arhaṇam


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.


One’s maternal uncle, the brother of one’s mother, is on the level of one’s father. When a maternal uncle has no son, his nephew legally inherits his property. Therefore, why did Kṛṣṇa directly kill Kaṁsa, the brother of His mother? Mahārāja Parīkṣit was very much inquisitive about the facts in this regard.