Valmiki Ramayana Yuddha Kanda Sarga 118 Shloka 13
Original Shlokaयत्कर्तव्यंमनुष्येणधर्षणांप्रतिमार्जता । तत्कृतंरावणंहत्वामयेदंमानकाङ्क्षिणा ।।6.118.13।।
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मानकाङ्क्षिणा that which my mind desired to do, मया by me, रावणम् Ravana, हत्वा killing, धर्षणाम् insult, प्रतिमार्जता to get rid of, मनुष्येण by a human, यत् all that, कर्तव्यम् duty, तत् that, इदम् thus, कृतम् done
"That which my mind desired as a duty of a human being, to get rid of the insult has been done by killing Ravana."