Shloka 6.84.15
निकुम्भिला-यज्ञविघ्नोपदेशः (Counsel to Disrupt the Nikumbhilā Rite)
तेनमोहयतानूनमेषामायाप्रयोजिता ।।।।विघ्नमन्विच्छतातत्रवानराणांपराक्रमे ।
caityaṃ nikumbhilāṃ nāma prāpya homaṃ kariṣyati |
hutavān upayāto hi devair api savāsavaiḥ ||
durādharṣo bhavaty eṣa saṅgrāme rāvaṇātmajaḥ ||
Reaching the sacred shrine called Nikumbhilā, Rāvaṇa’s son will perform the homa, the fire-offering. Having completed it and returned, he becomes exceedingly hard to assail in battle—even for the gods with Vāsava (Indra).
"Knowing the prowess of Vanaras, thinking surely that they will create obstacles for the ritual, he used the trick to keep them away (to be sad and not inclined for war)."
Dharma in warfare includes timely prevention of unjust advantage gained through harmful rites and deception; righteous strategy must counter adharma before it becomes unstoppable.
Vibhīṣaṇa informs Rāma that Indrajit is heading to Nikumbhilā to complete a rite that will make him nearly invincible in battle.
Prudent foresight (nīti) allied with truthfulness: Vibhīṣaṇa gives actionable intelligence to protect the righteous cause.