Bhagavad Gita Chapter 2.38
sukha-duḥkhe same kṛtvā
lābhālābhau jayājayau
tato yuddhāya yujyasva
naivaḿ pāpam avāpsyasi
Translation
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.