Valmiki Ramayana Aranya Kanda Sarga 54 Shloka 3
Original Shlokaवस्त्रमुत्सृज्य तन्मध्ये निक्षिप्तं सहभूषणम्।।3.54.3।। सम्भ्रमात्तु दशग्रीवस्तत्कर्म न स बुद्धवान्।
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सहभूषणम् along with ornaments, वस्त्रम् clothes, उत्सृज्य discarding, तन्मध्ये in their midst, निक्षिप्तम् thrown down, सः दशग्रीवः that tenheaded Ravana, सम्भ्रमात् due to excitement, तत् that, कर्म action of Sita, न बुद्धवान् did not know.
In his excitement Ravana failed to notice when Sita dropped down that garment along with ornaments in their midst.