Mbh 3.273.4

“The pious Vibhishana, O King, treading in the path followed by the virtuous and possessed of great glory, followed Kuvera. That adorable Lord of wealth, highly pleased with his younger brothers, invested him with the command of the Yaksha and Raksha hosts. On the other hand, the powerful and man-eating Rakshasas and Pisachas, having assembled together, invested the Ten-headed Ravana with their sovereignty. And Ravana, capable of assuming any form at will and terrible in prowess, and capable also of passing through the air, attacked the gods and the Daityas and wrested from them all their valuable possessions. And as he had terrified all creatures, he was called Ravana. And Ravana, capable of mustering any measure of might inspired the very gods with terror.”