Valmiki Ramayana Aranya Kanda Sarga 31 Shloka 12
Original Shlokaअकम्पनवच श्रुत्वा रावणो राक्षसाधिपः। नागेन्द्र इव निश्वस्य वचनं चेदमब्रवीत्।।3.31.12।।
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राक्षसाधिपः lord of the demons, रावणः Ravana, अकम्पनवचः Akampana's words, श्रुत्वाः having heard, नागेन्द्रः इव like the king of serpents, निश्वस्य after sighing heavily, इदम् these, वचनं च words too, अब्रवीत् said.
Having heard Akampana's words, Ravana, the lord of demons, sighed heavily like the king of serpents and said these words: