Bg 2.38

sukha-duhkhe same krtva
labhalabhau jayajayau
tato yuddhaya yujyasva
naivam papam avapsyasi

Word for word: 
sukha — happiness; duhkhe — and distress; same — in equanimity; krtva — doing so; labha-alabhau — both profit and loss; jaya-ajayau — both victory and defeat; tatah — thereafter; yuddhaya — for the sake of fighting; yujyasva — engage (fight); na — never; evam — in this way; papam — sinful reaction; avapsyasi — you will gain.

Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
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.

Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Lord Krishna now directly says that Arjuna should fight for the sake of fighting because He desires the battle. There is no consideration of happiness or distress, profit or loss, victory or defeat in the activities of Krishna consciousness. That everything should be performed for the sake of Krishna is transcendental consciousness; so there is no reaction to material activities. He who acts for his own sense gratification, either in goodness or in passion, is subject to the reaction, good or bad. But he who has completely surrendered himself in the activities of Krishna consciousness is no longer obliged to anyone, nor is he a debtor to anyone, as one is in the ordinary course of activities. It is said:

devarsi-bhutapta-nrnam pitrnam
na kinkaro nayam rni ca rajan
sarvatmana yah saranam saranyam
gato mukundam parihrtya kartam

“Anyone who has completely surrendered unto Krishna, Mukunda, giving up all other duties, is no longer a debtor, nor is he obliged to anyone – not the demigods, nor the sages, nor the people in general, nor kinsmen, nor humanity, nor forefathers.” (Bhag. 11.5.41) That is the indirect hint given by Krishna to Arjuna in this verse, and the matter will be more clearly explained in the following verses.