Chapter 2 · The Yoga of Knowledge · Krishna said
Bhagavad Gita 2.33 — Avoiding duty brings sin
अथ चेत्त्वमिमं धर्म्यं संग्रामं न करिष्यसि। ततः स्वधर्मं कीर्तिं च हित्वा पापमवाप्स्यसि ॥
atha cettvamimaṃ dharmyaṃ saṃgrāmaṃ na kariṣyasi | tataḥ svadharmaṃ kīrtiṃ ca hitvā pāpamavāpsyasi ||
Meaning
But if you do not fight this righteous war, you will give up your duty and your honour, and you will incur sin.