Canto 3 -
Araṇya-kāṇḍa
Chapter 43: Sītā Sees the Magical Deer
Text 3.43.18

भरतस्यार्यपुत्रस्य श्वश्रूणां मम च प्रभो।
मृगरूपमिदं व्यक्तं विस्मयं जनयिष्यति॥

bharatasyārya-putrasya śvaśrūṇāṁ mama ca prabho
mṛgarūpam idaṁ vyaktaṁ vismayaṁ janayiṣyati

bharatasya = Bharata; ārya-putrasya = You; śvaśrūṇām = mothers-in-law; mama = my; ca = and; prabho = O Lord; mṛgarūpam = excellent deer; idam = this; vyaktam = certainly; vismayam janayiṣyati = will astonish.

O Lord, this excellent deer will certainly astonish Bharata, You and my mothers-in-law.1

In the next verse, Sītā-devī states its use even if it cannot be caught alive.

1 Rāmāyaṇa-bhūṣaṇa: ārya-putrasya tava. mṛgarūpaṁ praśasta-mṛgaḥ. praśaṁsāyāṁ rūpap-pratyayaḥ. mṛgasya rūpaṁ vā.