Srimad-Bhagavatam: Canto 10 - Chapter 1 - Verse 12
Sanskrit:
किं मया हतया मन्द जात: खलु तवान्तकृत् ।यत्र क्व वा पूर्वशत्रुर्मा हिंसी: कृपणान् वृथा ॥ १२ ॥
ITRANS:
kiṁ mayā hatayā mandajātaḥ khalu tavānta-kṛtyatra kva vā pūrva-śatrurmā hiṁsīḥ kṛpaṇān vṛthā
Translation:
O Kaṁsa, you fool, what will be the use of killing me? The Supreme Personality of Godhead, who has been your enemy from the very beginning and who will certainly kill you, has already taken His birth somewhere else. Therefore, do not unnecessarily kill other children.