Valmiki Ramayana Ayodhya Kanda Sarga 73 Shloka 9
Original Shlokaननुत्वार्योऽपि धर्मात्मा त्वयि वृतिमनुत्तमाम्। वर्तते गुरुवृत्तिज्ञो यथा मातरि वर्तते।।2.73.9।।
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धर्मत्मा righteous, गुरुवृत्तिज्ञः well aware of his duties towards elders, आर्योऽपि noble, too मातरि towards his mother, यथा as, वर्तते conducted himself, त्वयि towards you, अनुत्तमाम् very great, वृत्तिम् conduct, वर्तते ननु is abiding indeed.
My noble and righteous brother (Rama), who is well aware of his duties to the elders conducted himself before you as he would before his own mother.