Valmiki Ramayana Yuddha Kanda Sarga 34 Shloka 24
Original Shlokaनोत्सहत्यमृतोमोक्तुंयुद्धेत्वामितिमैथिली: । सामात्यस्यनृशंसस्यनिश्चयोह्येषवर्तते ।।6.34.24।।
1 source checked for this shloka
मैथिली Mythili, युद्धे in combat, अमृतः from the other world, त्वाम् to you, मोक्तुम् to liberate, नोत्सहति not interested, इति this, एषः his option, सामात्स्य with his ministers नृशंसस्य no doubt, निश्चयः certainly, वर्तते not leave.
"O Mythili! Ravana is not interested in liberating you unless he goes to the other world in combat. (It can't happen when he is alive) This is certain. There is no doubt about this."