Bhagavad Gita 2.31

स्वधर्ममपि चावेक्ष्य न विकंपितुमर्हसि |
धर्म्याधि युद्धाच्छ्रेयोऽन्यत्क्षत्रियस्य न विद्यते

Translation

Besides, considering your duty as a warrior, you should not waver. Indeed, for a warrior, there is no better engagement than fighting for upholding of righteousness.