Bhagavad Gita 2.33

Refuse to fight in this righteous cause, and you will be a traitor, losing fame, incurring only sin.

अथ चैत्त्वमिमं धर्म्यं संग्रामं न करिष्यसि।
ततः स्वधर्मं कीर्तिं च हित्वा पापमवाप्स्यसि॥

atha caittvamimaṃ dharmyaṃ saṃgrāmaṃ na kariṣyasi|
tataḥ svadharmaṃ kīrtiṃ ca hitvā pāpamavāpsyasi||

English translation (above): Shri Purohit Swami (1935), public domain. Sanskrit text via github.com/gita/gita (Unlicense).