Valmiki Ramayana Ayodhya Kanda Sarga 1 Shloka 7
Original Shlokaस हि देवैरुदीर्णस्य रावणस्य वधार्थिभिः। अर्थितो मानुषे लोके जज्ञे विष्णुस्सनातनः।।2.1.7।।
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सनातन: the eternal, विष्णु: Visnu, उदीर्णस्य रावणस्य arrogant Ravana's, वधार्थिभि: by those desirous of slaying, देवै: by devatas, अर्थित: entreated, मानुषे लोके in the mortal world, स: he (Rama), जज्ञे हि was born indeed.
Entreated by the devatas desirous of slaying arrogant Ravana, the eternal Visnu was indeed born in the mortal world as Rama.