Valmiki Ramayana Kishkindha Kanda Sarga 40 Shloka 68
Original Shlokaअधिगम्य तु वैदेहीं निलयं रावणस्य च।।4.40.68।। मासे पूर्णे निवर्तध्वमुदयं प्राप्य पर्वतम्।
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उदयं पर्वतम् the mountain behind which the sun rises, प्राप्य after reaching, वैदेहीम् for Vaidehi, रावणस्य Ravana's, निलयं च home, अधिगम्य after reaching, मासे in one month, पूर्णे before completion, निवर्तध्वम् you may return.
'Reaching the mountain behind which the sun rises, look for Vaidehi and the home of Ravana and return by the month's end.