Valmiki Ramayana Sundara Kanda Sarga 27 Shloka 21
Original Shlokaन हि रामो महातेजाश्शक्यो जेतुं सुरासुरैः। राक्षसैर्वापि चान्यैर्वा स्वर्गः पापजनैरिव।।5.27.21।।
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महातेजाः very brilliant, रामः Rama, सुरासुरैः by gods and demons, राक्षसैर्वापि and even by demons, अन्यैर्वा and others also, स्वर्गः heaven, पापजनैरिव like sinners, जेतुम् to win, न शक्यः not possible.
"Just as a sinner cannot attain heaven Rama cannot be won by gods or demons, even rakshasas and others.