Valmiki Ramayana Ayodhya Kanda Sarga 100 Shloka 16
Original Shlokaमन्त्रो विजयमूलं हि राज्ञां भवति राघव। सुसंवृतो मन्त्रधरैरमात्यै श्शास्त्रकोविदैः।।2.100.16।।
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राघव O Bharata, शास्त्रकोविदैः by men learned in scriptures, मन्त्रधरैः by those who can withhold proper counselling, अमात्यैः by ministers, सुसंवृतः wellguarded, मन्त्रः advice, राज्ञाम् to the king, विजयमूलम् root of victory, भवति हि will become.
O Bharata the wellguarded advice of ministers, learned in scriptures and capable of proper counselling, is the root of victory for kings, specially when the advice is kept in confidence.