Valmiki Ramayana Yuddha Kanda Sarga 71 Shloka 102
Original Shlokaन शशाकरुजंकर्तुंयुधितस्यनरोत्तमः । अथैनमभ्युपागम्यवायुर्वाक्यमुवाच ह ।।6.71.102।।
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नरोत्तमः best of men, युधि in battle, रुजम् to injure, कर्तुम् to do, न शशाक not be killed, अथ now, वायुः Vayu, एनम् in that way, उपागम्य having come, वाक्यम् words, उवाच ह spoke to him.
Wind god (Vayu) having come to the best of men, Lakshmana, spoke to him that in battle it is not possible to injure him or kill him.