Valmiki Ramayana Yuddha Kanda Sarga 59 Shloka 115
Original Shlokaतेनमुष्टिप्रहारेणरावणोराक्षसेश्वरः । जानुभ्यामपतद्भूमौचचालचपपातच ।।6.59.115।।
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तेन by that, मुष्टिप्रहारेण blow of the fist, राक्षसेश्वरः Rakshasa Lord, रावणः Ravana, चचाल shaken, जानुभ्याम् on his knees, भूमौ on the ground, अपतत् च fell.
By the blow of Hanuman's fist, Ravana the Lord of Rakshasas was shaken and fell on the ground on his knees.