Bhagwad Gita
Chapter 2, Verse 38
सुखदुःखे समे कृत्वा लाभालाभौ जयाजयौ।
ततो युद्धाय युज्यस्व नैवं पापमवाप्स्यसि।।2.38।।
Do thou fight for the sake of fighting, without considering happiness or distress, loss or gain, victory or defeat—and, by so doing, you shall never incur sin.