The Deserter - S1.E16

Aang and his friends go to a Fire Nation town so that Aang can witness some firebending, but their plan soon goes awry when it’s discovered that he is the Avatar. Fortunately, he's rescued by an individual who serves a firebending master named Jeong Jeong who has abandoned the Fire Nation, so Aang decides to use this time to attempt to learn firebending. The firebending master, however, seems reluctant to teach Aang.