Dragon Ball Z - episode 5 - 23 May, 1989

As Goku takes blow after punishing blow from the evil Raditz, Gohan is able to watch no longer! The young boy's rage unlocks an awesome power sleeping within him, and he unleashes a mighty attack that not even Radtiz can resist! But as quickly as Gohan's power appears, it vanishes. And when Raditz prepares to strike back, Goku must make the ultimate sacrifice to save his son! This all only leads to the revelation that two more Saiyans are on their way to Earth. (Source: dbzepisode.org)