Avatar: The Last Airbender Season 2 Episode 11 : The Desert
The gang is stranded in the desert, helpless without Appa. A secret society helps protect Iroh and Zuko from the Fire Nation. While there, they are recognized by the men hired by Toph's father, who plan to capture them for the reward. After going through the many perils of the desert, Aang tracks down the Sandbenders who stole Appa, and learns that Appa was traded to a merchant in Ba Sing Se. Upon hearing that Appa was muzzled, Aang becomes so mad that he enters the Avatar State, almost wiping out the Sandbenders, but is calmed down by Katara.