Valmiki Ramayana Yuddha Kanda Sarga 18 Shloka 26

परन्तप scorcher of enemies, बद्धाञ्जलिपुटम् who greets reverentially with folded hands, दीनम् piteous, याचन्तम् begs, शरणागतम् protection, शत्रुम् अपि even the enemy, अनृशंस्यार्थम् not to be cruel नहन्यात् not to be killed.

"O scorcher of enemies To one who greets reverentially with folded hands and begs for protection, we should not be cruel, and he is not to be killed."