Dragon Ball Z - episode 35 - 06 Feb, 1990

Vegeta attempts to finish off Gohan to prevent him from looking at his artificial moon and transforming when Yajirobe jumps in and stops him by cutting through his armor with his sword, resulting in a heroic distraction. As Vegeta pummels Yajirobe for his interference, Gohan recovers, and then on Goku's telepathic commands, he looks at Vegeta's moon and transforms into a Great Ape. However, unlike Vegeta, Gohan can't control himself in this state. Alerted quickly by Goku and Krillin's cries for him to defeat Vegeta, Gohan quickly regains some of his consciousness and resumes the fight, pounding on Vegeta. Vegeta is able to cut off Gohan's tail in midair, but as Gohan falls to Earth he lands on and crushes the Saiyan Prince before finally reverting to his normal form. Defeated and severely injured, Vegeta pulls out his remote and summons his spaceship. As he crawls toward it, Krillin attempts to kill him with Yajirobe's kitana. Goku tells Krillin to stop and let Vegeta go, hoping that the act of mercy can change the Saiyan Prince. His life spared, Vegeta promises the surviving Z Fighters that he will return and have his revenge as he leaves Earth in his spaceship for good. The Battle for Earth ends in victory for the Z Fighters, but at the cost of the lives of Piccolo, Yamcha, Tien, Chiaotzu and Kami as well as Earth's Dragon Balls. (Source: Wikipedia)