Valmiki Ramayana Yuddha Kanda Sarga 21 Shloka 5
Original Shlokaशयनेचोत्तमाङ्गेनसीतायाश्शोभितंपुरा । तक्षकस्येवसम्भोगगङ्गाजलनिषेचितम् ।।6.21.5।।
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पुरा earlier, शयने while he slept, सीतायाः Sita's, उत्तमाङ्गेन the best of women, शोभितम् graced, गङ्गाजलनिषेवितम् given bath with waters of Ganga, तक्षकस्य Takshaka's, सम्भोगमिव as if united in delight.
(The shoulders) which resembled the coils of Takshaka (in chubbiness) a principal serpent, was graced by Sita while in bed, was bathed by the best of women with waters of Ganga.