Valmiki Ramayana Yuddha Kanda Sarga 5 Shloka 18
Original Shlokaस्वभावतनुकानूनंशोकेनानशनेनच । भूयस्तनुतरासीतादेशकालविपर्ययात् ।।6.5.18।।
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स्वभावतनुका: by nature slim, सीता: Sita, देशकालविपर्ययात्: due to unfavorable time and space, शोकेन: in grief, अनशनेन: due to abstaining from eating, नूनम्: surely, भूयः would be, तनुतरा: slender
Sita who is by nature slim would surely be slender due to abstaining from eating, unfavorable time and location.