Other source:
Kami revives Shenron, the Eternal Dragon. When Goku's friends down on Earth call Shenron, he tells them that Goku is training in Heaven under Kami-sama and will meet them at the next Martial Arts Tournament. They wish for everyone who was killed by Piccolo to be revived. The news that Goku is training under Kami spurs Tienshinhan, Yamcha, and Krillin to train hard as well for the competition.
