Tumharo mantra Bibhishan mana: meaning
Chaupai 17 of the Hanuman Chalisa
तुम्हरो मंत्र बिभीषन माना
लंकेस्वर भए सब जग जाना
tumharo mantra Bibhīṣan mānā / Laṅkesvar bhae sab jag jānā
Vibhishana took your advice, and became lord of Lanka, as the whole world knows.
Words
तुम्हरो tumharoyour
मंत्र mantraadviceSanskrit mantra means counsel as well as a sacred formula.
बिभीषन BibhīṣanVibhishana
माना mānāaccepted
लंकेस्वर Laṅkesvarlord of LankaLaṅkā plus Sanskrit īśvara, lord.
भए bhaebecame
सब saball
जग jagthe world
जाना jānāknows
Vibhishana changes sides
Ravana's brother Vibhishana leaves Lanka to join Ram. In Tulsidas, Hanuman meets him inside Lanka and they talk before he goes. In Valmiki, Hanuman speaks up for accepting him when Ram's camp debates whether he can be trusted. After Ravana's death, Vibhishana is crowned.
Source: Tulsidas, Ramcharitmanas, Sundar Kand; Valmiki Ramayana, Yuddha Kanda