Srimad-Bhagavatam: Canto 9 - Chapter 1 - Verse 38
Sanskrit:
राम राम महाबाहो भवान् पापमकारषीत् ।अवधीन्नरदेवं यत्सर्वदेवमयं वृथा ॥ ३८ ॥
ITRANS:
rāma rāma mahābāhobhavān pāpam akāraṣītavadhīn naradevaṁ yatsarva-devamayaṁ vṛthā
Translation:
O great hero, my dear son Paraśurāma, you have unnecessarily killed the king, who is supposed to be the embodiment of all the demigods. Thus you have committed a sin.