Valmiki Ramayana Yuddha Kanda Sarga 12 Shloka 35
Original Shlokaतस्मात्त्वयासमारब्धंकर्मह्यप्रतिमंपरैः । अहंसमीकरिष्यामिहत्वाशत्रूंस्तवानघ ।।6.12.35।।
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आनघ: sinless one, तस्मात् therefore, त्वया: by you, परैः other than me, समारब्दम् undertaking, अप्रतिमम् which is not possible, कर्म: act अहम् I, तव: your, शत्रून् enemy, हत्वा: killing, समीकरिष्यामि: accomplish your goal.
"O Sinless Ravana Therefore, that which you have done is not possible for none other than me. I will kill your enemy and accomplish your goal for you."