Valmiki Ramayana Yuddha Kanda Sarga 37 Shloka 8
Original Shlokaभूत्वाशकुनयस्सर्वेप्रविष्टाश्चरिपोर्भलम् । विधानंविहितंयच्चतद्धृष्टवासमुपस्थिताः ।।6.37.8।।
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सर्वे all, शकुनयः birds, भूत्वा form, रिपोः enemy, बलम् strength, प्रविष्टाः went in deep, यत् , विधानम् arrangements, विहितम् knowing, तत् there, दृष्टवा seeing, समुपस्थिताः turned up.
All of them assumed the form of birds and went deep into Lanka, saw the enemy strength and arrangements made by the enemy and turned up.