Canto 3 -
Araṇya-kāṇḍa
Chapter 43: Sītā Sees the Magical Deer
Text 3.43.39

उत्थाय बहवो येन मृगयायां जनाधिपाः।
निहताः परमेष्वासास्तस्माद्वध्यस्त्वयं मृगः॥

utthāya bahavo yena mṛgayāyāṁ janādhipāḥ
nihatāḥ parameṣvāsās tasmād vadhyas tv ayaṁ mṛgaḥ

utthāya = appeared; bahavaḥ = many; yena = he; mṛgayāyām = while hunting; jana-adhipāḥ = who ruled over men; nihatāḥ = and killed; parama-iṣvāsāḥ = excellent bowmen; tasmāt = so; vadhyaḥ tu = must be killed; ayam = this; mṛgaḥ = deer.

He appeared and killed many excellent bowmen who ruled over men while hunting. So this deer must be killed.