Valmiki Ramayana Yuddha Kanda Sarga 70 Shloka 43
Original Shlokaसतलाभिहतस्तेनस्रस्तहस्तायुधोभुवि । निपपातमहातेजास्त्रिशिरास्त्यक्तचेतनः ।।6.70.43।।
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महातेजाः highly energetic, सःत्रिशिराः that Trisira, तेन by that, तलाभिहतः hit by palm, स्रस्तहस्तायुधः weapon dropped from hand, त्यक्तचेतनः senses lost, भुवि ground, निपपात fell.
Trisira, a highly energetic one, hit by Hanuman with his palm, dropped the weapon from his hand, lost his senses and fell on the ground.