The Bodhisatta was once a naga. His father was a wise naga king and his younger brother was cruel and hot-headed, always getting in trouble. One time after the brother struck some female nagas, his father got so angry he ordered him expelled, but the Bodhisatta convinced him to change his mind. The same thing happened a second time, but after the third time the father was so fed up he ordered both the brother and the Bodhisatta to go to the city and live on a dung heap for three years; and this time his mind could not be changed.
When some boys saw the pair scrounging for food they mocked them and threw sticks and things at them. The younger brother was furious about this disrespect and told the Bodhisatta they should go kill them with their venomous breath. The Bodhisatta calmed him down and explained that they were in a foreign land and nobody there knew about their rank, so they had no choice but to endure abuse from low-class people. This was an important lesson for the brother, and after the exile was over he returned home with a humbler heart.
In the Lifetime of the Buddha
The younger naga brother was an earlier birth of one of the Buddha’s disciples who had a bad temper. The Buddha told him this story so he knew he had been the same in the past and had overcome the problem.