Valmiki Ramayana Ayodhya Kanda Sarga 111 Shloka 3
Original Shlokaपिता ह्येवं जनयति पुरुषं पुरुषर्षभ। प्रज्ञां ददाति चाचार्यस्तस्मात्स गुरुरुच्यते।।2.111.3।।
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पुरुषर्षभ O best of men, एवं पुरुषम् in such a way a man, पिता father, जनयति हि begets, आचार्यः teacher, प्रज्ञाम् wisdom, ददाति gives, तस्मात् therefore, सः that (teacher), गुरुः become guru, उच्यते is called.
O best of men, the father brings forth a son. The teacher imparts him wisdom. Therefore, the teacher is considered superior.