Valmiki Ramayana Ayodhya Kanda Sarga 37 Shloka 34
Original Shlokaअथोत्तमान्याभरणानि देवि देहि स्नुषायै व्यपनीय चीरम्। न चीरमस्याः प्रविधीयतेति न्यवारयत्तद्वसनं वसिष्टः।।2.37.34।।
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अथ then, देवि Devi (Kaikeyi), चीरम् bark robes, व्यपनीय having removed, स्नुषायै your daughterinlaw, उत्तमानि precious, आभरणानि ornaments, देहि give, अस्याः her, चीरम् bark robes, न प्रविधीयत was not decided, इति thus, वसिष्ठः Vasistha, तत् that, वसनम् garment, न्यवारयत् prevented.
O Kaikeyi remove those bark robes and bestow on your daughterinlaw precious ornaments. She was not ordained to wear the bark. Vaisishta, saying so, prevented Sita from wearing that garment.