Valmiki Ramayana Bala Kanda Sarga 2 Shloka 41
Original Shlokaतस्य बुद्धिरियं जाता वाल्मीकेर्भावितात्मन: । कृत्स्नं रामायणं काव्यमीदृशै: करवाण्यहम् ।।1.2.41।।
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अहम् I, कृत्स्नम् entire, रामायणम् named Ramayana, काव्यम् poem, ईदृशै: in this metre, करवाणि shall compose, इयम् बुद्धि: this thought, भावितात्मन: who is capable of putting thoughts into action, तस्य (महर्षे:) वाल्मीकेः to Valmiki, जाता occurred.
A thought occurred to Valmiki, who is capable of putting thoughts into action "I shall compose the epic named Ramayana entirely in this metre".