Shloka 6.85.16
निकुम्भिला-यज्ञविघ्नः — Vibhishana’s Counsel and Lakshmana’s March to Nikumbhila
वधायेन्द्रजितोरामसन्दिशस्वमहाबल ।हतेतस्मिन्हतंविद्धिरावणंससुहृज्जनम् ।।6.85.16।।
vadhāyendrajito rāma sandiśasva mahābala | hate tasmin hataṃ viddhi rāvaṇaṃ sasuhṛjjanam ||
O Rama, of extraordinary might! Command the destruction of Indrajit. Know that when he is slain, Ravana too—along with his kinsmen and allies—is as good as dead.
Rama, you are endowed with extraordinary prowess! Order now for the destruction of Indrajith as with his death Ravana and all his kinsfolk are killed, you may know.
Indrajit was the most formidable warrior of Lanka and Ravana's primary shield. Vibhishana implies that without Indrajit, the morale and defense of the Rakshasas would collapse, making Ravana's defeat inevitable.
This verse marks the critical turning point where the secret to defeating Indrajit (interrupting his Nikumbhila Yajna) is acted upon, shifting the momentum of the war in favor of Rama.