Valmiki Ramayana Ayodhya Kanda Sarga 26 Shloka 29
Original Shlokaयाते च मयि कल्याणि वनं मुनिनिषेवितम्। व्रतोपवासपरया भवितव्यं त्वयाऽनघे।।2.26.29।।
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अनघे O sinless one, कल्याणि O auspicious one, मयि me, मुनिनिषेवितम् inhabited by ascetics, वनम् to the forest, याते when I am gone, त्वया by you, व्रतोपवास परया engaged in vratas and fasting, भवितव्यम् should be done.
O sinless, auspicious one engage yourself in vratas and fasting after my departure to the forest inhabited by ascetics.