Valmiki Ramayana Aranya Kanda Sarga 31 Shloka 27
Original Shlokaन हि रामो दशग्रीव शक्यो जेतुं त्वया युधि। रक्षसां वापि लोकेन स्वर्गः पापजनैरिव।।3.31.27।।
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दशग्रीव O tenheaded one, रामः Rama, युधि in war, त्वया by you, रक्षसाम् of demons, लोकेन by the world, वापि or ever, जेतुम् to win, स्वर्गः heaven, पापजनैरिव by sinners, न शक्यः not possible.
O tenheaded one, just as it is not possible for sinners to attain heaven it is not possible for you or for the entire world of demons to win him in war