Valmiki Ramayana Kishkindha Kanda Sarga 48 Shloka 20
Original Shlokaतमापतन्तं सहसा वालिपुत्रोऽङ्गदस्तदा। रावणोऽयमिति ज्ञात्वा तलेनाभिजघान ह।।4.48.20।।
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तदा then, वालिपुत्रः Vali's son, अङ्गदः Angada, आपतन्तम् pouncing, तम् them, अयम् this person, रावणः is Ravana, इति thus, ज्ञात्वा on thinking, सहसा at once, तलेन with his palm, अभिजघान ह slapped him.
Mistaking him for Ravana, Angada, Vali's son at once pounced on him and slapped him with his palm.