Sanskrit

श्रेयान्स्वधर्मो विगुणः परधर्मात्स्वनुष्ठितात्। स्वधर्मे निधनं श्रेयः परधर्मो भयावहः।।3.35।।

Summary

It is better to do one's own duty, however lacking in merit, than to do that of another, even though efficiently. It is better to die doing one's own duty, for doing the duty of another is fraught with danger.