Valmiki Ramayana Sundara Kanda Sarga 37 Shloka 55
Original Shlokaकामं त्वमसि पर्याप्तो निहन्तुं सर्वराक्षसान्। राघवस्य यशो हीयेत्त्वया शस्तैस्तु राक्षसैः।।5.37.55।।
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त्वम् you, सर्वराक्षसान् all the ogres, निहन्तुम् to slay, पर्याप्तः अपि कामम् it may be you can do the task, त्वया by you, शस्तै by those killed, राक्षसैः by demons, राघवस्य Rama's, यशः fame, हीयेत् will diminish.
"It may be that you can kill all the demons but by such an act the fame of Rama will be diminished. (He cannot give his strength a trial)