When there's dissent among everyone whether to offer refuge to Vibhīṣaṇa or not, Rāma narrates a story of how a bird offers itself as food to a hungry fowler by jumping into fire.
It is narrated how by a dove, its enemy (a fowler) when it came for a refuge, was received according to rules of hospitality and was invited for a feast with its own flesh. O, the excellent of monkeys! The aforesaid dove indeed accepted as a guest, the fowler as he came, although he killed its wife. How much more a man like me has to do? Hear the verses inculcating virtue so long ago, by Kandu, the son of a sage called Kanva, a great sage and a speaker of truth. O, Sugreeva, even an enemy, who formed a cup with his hollowed hands, a miserable person, a person who is begging and who is seeking a refuge should not be killed with the aim of not being cruel. An enemy who comes for protection against others, even if the aforesaid enemy is oppressed or arrogant, is to be protected by one who has a disciplined mind, even by abandoning one's life. If he does not protect rightly through his strength, by fear or by ignorance or by desire, it is a sin to be reproached by the world. If having not been protected, a refugee dies before the eyes of a man who is able to protect him, the former takes along all his moral merit and goes. In not protecting thus the persons who take refuge, there is a great blemish involved in it. It does not bestow heaven. It destroys reputation. It devastates strength and valor. I will follow the excellent words of Kandu. It becomes a very righteous thing, gives reputation, leads to heaven and the rewards appear consequently. He who seeks refuge in me just once, telling me that 'I am yours', I shall give him assurance of safety against all types of beings. This is my solemn pledge. O, Sugreeva, the chief of monkeys! Let him either be Vibhishana or even Ravana himself; I have given an assurance of safety to him. Bring him here.