Valmiki Ramayana Sundara Kanda Sarga 34 Shloka 9
Original Shlokaयथा यथा समीपं स हनुमानुपसर्पति। तथा तथा रावणं सा तं सीता परिशङ्कते।।5.34.9।।
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सः हनुमान् Hanuman, यथा यथा slowly that way, समीपम् near, उपसर्पति started moving, तथा तथा in the same way, सा सीता that Sita, तम् him, रावणम् Ravana, परिशङ्कते suspected.
As Hanuman started slowly drawing close, Sita suspected he might be Ravana.