Valmiki Ramayana Ayodhya Kanda Sarga 9 Shloka 61
Original Shlokaप्रपत्स्यते राज्यमिदं हि राघवो यदि ध्रुवं त्वं ससुता च तप्स्यसे। अतो हि कल्याणि यतस्व तत्तथा यथा सुतस्ते भरतोऽभिषेक्ष्यते।।2.9.61।।
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राघव: descendant of the Raghus (Rama), इदम् हि this indeed, राज्यम् kingdom, प्रपत्स्यते यदि if secures, ससुता along with son, त्वम् you, तप्स्यसे you will suffer, ध्रुवम् this is true, कल्याणि auspicious one, अत: for that reason, ते सुत: your son, भरत: Bharata, यथा in a manner in which, अभिषेक्ष्यते will be installed, तत् that act, तथा in that way, यतस्व strive for.
It is true that if Rama secures this kingdom, you along with your son are bound to suffer. O auspicious one, hence act in a way your son Bharata will be installed.