Valmiki Ramayana Ayodhya Kanda Sarga 4 Shloka 23
Original Shlokaतस्मात्त्वयाऽद्य प्रभृति निशेयं नियतात्मना। सह वध्वोपवस्तव्या दर्भप्रस्तरशायिना।।2.4.23।।
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तस्मात् therefore, अद्यप्रभृति from now, इयम् this, निशा night, नियतात्मना with selfrestraint, दर्भप्रस्तरशायिना sleeping on a bed of darbha or kusha grass, त्वया by you, वध्वा सह with daughterinlaw, Sita, उपवस्तव्या should be spent by undertaking fasting.
Therefore, you and my daughterinlaw (Sita) should fast tonight and sleep on a bed of darbha or kusha grass with selfrestraint.