Valmiki Ramayana Yuddha Kanda Sarga 112 Shloka 18
Original Shlokaनैकान्तविजयोयुद्धेभूतपूर्वःकदाचन । परैराहन्यतेवीरःपरान्वाहन्तिसंयुगे ।।6.112.18।।
1 source checked for this shloka
कदाचन not only that, युद्धे in war, एकान्तविजयः victorious alone, न भूतपूर्वः now or before, वीरः heroic, संयुगे in war, परैः enemy, हन्यतेवा will kill, परान् by enemy, हन्तिवा be killed
"Not only that, in war, he will only will be victorious is not true now or before. Hero may kill the enemy or will be killed by the enemy."