Valmiki Ramayana Sundara Kanda Sarga 35 Shloka 84
Original Shlokaएवं विश्वासिता सीता हेतुभिश्शोककर्शिता। उपपन्नैरभिज्ञानैर्दूतं तमवगच्छति।।5.35.84।।
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शोककर्शिता tormented by grief, सीता Sita, एवम् in that way, हेतुभिः with possible reasons, विश्वासिता having trusted, उपपन्नैः by the evidences, अभिज्ञानैः with identification, तम् him, दूतम् as a messenger, अवगच्छति she understood.
The griefstricken Sita trusted him by his logical presentation of reasons as well as identifications. She believed that he was a messenger (of Rama).