Valmiki Ramayana Yuddha Kanda Sarga 36 Shloka 21

राक्षसपुङ्गवः best of Rakshasas, लङ्कायाः in Lanka, एवम् in that way, विधानम् order, कृत्वा having done, कालचोदितः sway of destiny, आत्मानम् his own, कृतकृत्यमिव as if accomplished the task, मन्यते thought.

The best of Rakshasas under the sway of destiny, having been ordered in that way in Lanka, Ravana felt as though he had accomplished the task.