Canto 3 -
Araṇya-kāṇḍa
Chapter 72: Kabandha Tells Rāma About Sugrīva
Text 3.72.26

स मेरुशृङ्गाग्रगतामनिन्दितां प्रविश्य पातालतलेऽपि वाश्रिताम्।
प्लवङ्गमानां प्रवरस्तव प्रियां निहत्य रक्षांसि पुनः प्रदास्यति॥

sa meru-śṛṅgāgra-gatām aninditāṁ
praviśya pātāla-tale ’pi vāśritām
plavaṅgamānāṁ pravaras tava priyāṁ
nihatya rakṣāṁsi punaḥ pradāsyati

saḥ = that; meru-śṛṅga-agra-gatām = she is on a peak of Mount Meru; aninditām = who is irreproachable in character; praviśya = will enter [the residence of Rāvaṇa]; pātāla-tale = Pātāla; api = even [if]; = or; āśritām = in; plavaṅgamānām = of the monkeys; pravaraḥ = best; tava = Your; priyām = beloved wife; nihatya = slay; rakṣāṁsi = the rākṣasas; punaḥ pradāsyati = and return.

That best of the monkeys will enter [the residence of Rāvaṇa], slay the rākṣasas and return Your beloved wife who is irreproachable in character, even [if] she is on a peak of Mount Meru or in Pātāla.

“Irreproachable in character” declares that Sītā-devī is pure.