Canto 1 - Boyhood
Bāla-kāṇḍa
Chapter 41: Aṁśumān Searches for His Uncles and the Horse
Text 1.41.3

अन्तर्भौमानि सत्त्वानि वीर्यवन्ति महान्ति च।
तेषां त्वं प्रतिघातार्थं सासिं गृह्णीष्व कार्मुकम्॥

antar-bhaumāni sattvāni vīryavanti mahānti ca
teṣāṁ
tvaṁ pratighātārthaṁ sāsiṁ gṛhṇīṣva kārmukam

antar-bhaumāni = that live within the earth; sattvāni = creatures; vīryavanti = powerful; mahānti = great; ca = and; teṣām tvam pratighāta-artham = to neutralize; sa-asim = and sword; gṛhṇīṣva = accept; kārmukam = this armor.

Accept this armor and sword to neutralize all heroic, great and powerful creatures that live within the earth.

“That live within the earth” refers to the creatures living within the cavities of the earth.