Valmiki Ramayana Ayodhya Kanda Sarga 9 Shloka 31
Original Shlokaचतुर्दश हि वर्षाणि रामे प्रव्राजिते वनम्। रूढश्च कृतमूलश्च शेषं स्थास्यति ते सुतः।।2.9.31।।
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रामे of Rama, चतुर्दश वर्षाणि for fourteen years, वनम् to the forest, प्रव्राजिते having been exiled, ते सुत: your son, रूढ: च will grow strong, कृतमूल: च and deeprooted, शेषम् for the remaining time, स्थास्यति shall remain (stable).
After Rama has been exiled into the forest for fourteen years your son grown strong and deeprooted will remain (king) for the rest of his life.