Valmiki Ramayana Ayodhya Kanda Sarga 104 Shloka 18
Original Shlokaकामकारो महाप्राज्ञ गुरूणां सर्वदाऽनघ। उपपन्नेषु दारेषु पुत्रेषु च विधीयते।।2.104.18।।
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महाप्राज्ञ sagacious, अनघ sinless, गुरूणाम् of elders, उपपन्नेषु when married, दारेषु in relation to their wives, पुत्रेषु च also sons, सर्वदा always, कामकारः acting at will, विधीयते is laid down.
O sagacious and sinless one, it is laid down (in sastras) that elders when married can always act at their free will towards their wives and sons.