Vibhishana Joins Rama and Crosses to Lanka
Vibhishana, the righteous brother of Ravana, meets Rama with his advisers after the bridge is built. Sugriva suspects he is a spy, but Rama satisfies himself about Vibhishana's truthfulness through his actions and conduct. He instates Vibhishana as king of the rakshasas and makes him Lakshmana's adviser. Following Vibhishana's instructions, Rama and his army cross the ocean within a month — and the campaign against Lanka begins.
Vibhishana, the brother of the Indra of the rakshasas and with dharma in his soul, met Rama there, with his advisers, and the great-souled one welcomed him.
Sugriva had his misgivings that he might be a spy. But Raghava satisfied himself about the truth through his actions, gestures, and conduct, and showed him the honours. He instated Vibhishana as the king of all the rakshasas and made him Lakshmana's adviser and well-wisher.
In accordance with Vibhishana's instructions, within a month, Rama, together with his army, crossed the ocean over the bridge. Then, having reached Lanka, he caused its many and large gardens to be ravaged by the monkeys.
Ravana had two rakshasa advisers named Shuka and Sarana. They disguised themselves as monkeys and came as spies, but Vibhishana had them caught. When those roamers of the night revealed their real forms of rakshasas, Rama had them shown to his army. Later, he let them go.
Having set up the quarters for his army in a grove in the city, the brave one sent the wise monkey Angada as his messenger to Ravana. Aranyaka Parva, Chapter 564