Valmiki Ramayana Ayodhya Kanda Sarga 36 Shloka 26
Original Shlokaइत्येनमत्यजद्राजा सगरो वै सुधार्मिकः। रामः किमकरोत्पापं येनैवमुपरुध्यते।।2.36.26।।
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सुधार्मिकः highly righteous, सगरः राजा king Sagara, इति thus, एनम् him, अत्यजत् abandoned, रामः Rama, किं पापम् what sin, अकरोत् has committed, येन by which, एवम् this way, उपरुध्यते should be banished.
Highly righteous king Sagara thus banished his son. What sin has Rama committed to secure a similar banishment?