Valmiki Ramayana Ayodhya Kanda Sarga 35 Shloka 35
Original Shlokaरामे हि यौवराज्यस्थे राजा दशरथो वनम्। प्रवेक्ष्यति महेष्वासः पूर्ववृत्तमनुस्मरन्।।2.35.35।।
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रामे Rama, यौवराज्यस्थे on being installed as heirapparent, महेष्वासः great archer, राजा king, दशरथः Dasaratha, पूर्ववृत्तम् the ancient custom, अनुस्मरन् recollecting, वनम् to the forest, प्रवेक्ष्यति enter.
If Rama is installed as heirapparent, king Dasaratha, the great archer will retire to the forest for carrying out austerities following ancient customs.