Srimad-Bhagavatam: Canto 3 - Chapter 1 - Verse 4
Sanskrit:
स तदा लब्धतीर्थोऽपि न बबाधे निरायुधम् ।मानयन् स मृधे धर्मं विष्वक्सेनं प्रकोपयन् ॥ ४ ॥
ITRANS:
sa tadā labdha-tīrtho ’pina babādhe nirāyudhammānayan sa mṛdhe dharmaṁviṣvaksenaṁ prakopayan
Translation:
Even though the demon had an excellent opportunity to strike his unarmed foe without obstruction, he respected the law of single combat, thereby kindling the fury of the Supreme Lord.