Canto 3 -
Araṇya-kāṇḍa
Chapter 3: Virādha Carries Rāma and Lakṣmaṇa
Text 3.3.7

तपसा चापि मे प्राप्ता ब्रह्मणो हि प्रसादजा।
शस्त्रेणावध्यता लोकेऽच्छेद्याभेद्यत्वमेव च॥

tapasā cāpi me prāptā brahmaṇo hi prasādajā
śastreṇāvadhyatā loke ’cchedyābhedyatvam eva ca

tapasā = by ascetic practice; ca api = moreover; me = I; prāptā = and become; brahmaṇaḥ hi = Lord Brahmā; prasādajā = have pleased; śastreṇa = by any weapon; avadhyatā = incapable of being killed; loke = in this world; acchedya-abhedyatvam eva ca = by being cut or pierced.

Moreover, by ascetic practice I have pleased Lord Brahmā and become incapable of being killed by being cut or pierced by any weapon in this world.1

GLOSS. [Acchedyābhedyatvam] also indicates that [his bodily] limbs would be unbreakable.1

1 Rāmāyaṇa-bhūṣaṇa: tapasā sādhanena. In other words, the rākṣasa had performed ascetic penance and satisfied Lord Brahmā who blessed him with the boon that he could not be killed by any weapon and that his life could not be taken away from his body by cutting or piercing his body.

1 Rāmāyaṇa-bhāva-dīpa: yadvā chedyānām aṅgānām abhedyatvam.