Valmiki Ramayana Sundara Kanda Sarga 15 Shloka 27
Original Shlokaह्रियमाणा तदा तेन रक्षसा कामरूपिणा।।5.15.27।। यथारूपा हि दृष्टा वै तथारूपेयमङ्गना।
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तदा then, कामरूपिणा by one who can assume any form at will, तेन रक्षसा by that demon, ह्रियमाणा being kidnapped, यथारूपा the same form, दृष्टा after seeing, इयम् this, अङ्गना lady, तथारूपा has the same form.
Beholding the form of the largeeyed lady, Hanuman guessed, 'This is similar to the form seen while the demon was kidnapping her'.