Valmiki Ramayana Aranya Kanda Sarga 56 Shloka 8
Original Shlokaअसुरैर्वा सुरैर्वा त्वं यद्यवध्योऽसि रावण। उत्पाद्य सुमहद्वैरं जीवंस्तस्य न मोक्ष्यसे।।3.56.8।।
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रावण O Ravana, त्वम् you, असुरैर्वा by demons, सुरैर्वा or by gods, अवध्यः are not to be killed, असि यदि even if, सुमहत् great, वैरम् enmity, उत्पाद्य after creating, जीवन् with life, तस्य his, न मोक्ष्यसे you will not be released.
O Ravana, even if you stand invulnerable to gods and demons, you will not come out alive in the combat with Rama with whom you have earned great enmity.