Valmiki Ramayana Aranya Kanda Sarga 61 Shloka 21
Original Shlokaतस्य शैलस्य सानूनि गुहाश्च शिखराणि च।।3.61.21।। निखिलेन विचिन्वानौ नैव तामभिजग्मतुः।
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तस्य शैलस्य that mountain's, सानूनि slopes, गुहाश्च caves also, शिखराणि च mountain peaks too, निखिलेन entirely, विचिन्वानौ searched, ताम् her, नैव अभिजग्मतुः were not able to find.
They were not able to find Sita even though they searched all over the mountain slopes, caves and peaks.