DB Chapter 197
From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
"Tails of Future Not-Quite-Past" (孫悟空の過去！！, Son Gokū no Kako!!; Literally meaning "Son Goku's Past!!") is chapter 197 of the Dragon Ball manga.
Goku freaks out about the tail, and the alien says Kakarrot's finally seeing his true form. Goku doesn't understand, and the alien thinks Kakarrot must've had a great shock to the head. Goku says he ain't this "Kaka-whatever", he's Son Goku. The dude yells to just answer the question, if he was hit on the head or not. Goku sort of remembers hitting his head when he was little, and he still has a scar.
Kame-Sen'nin says that he had heard Son Gohan had taken in a baby with a tail and a wild personality. "But, one day, he accidentally dropped the baby in a valley, hitting its head really hard. He almost died, but the baby had an unbelievable life force, and it seems the baby was saved. Additionally, after that, the wild personality disappeared and he became an obedient, good boy..." Goku realizes that baby was him, and Bulma wonders what this means, is this alien somehow connected to Goku?
The alien realizes Kakarrot has forgotten everything, as Kuririn gets up and warns Goku about how strong he is. "I'll explain it to you! First, you are not a human of this planet!! You were born on Planet Vegeta!! You're of the prideful, strongest race in all the universe, the Saiyans!!! And, I am your older brother, Raditz!!!" Everyone freaks out, and Goku thinks this is nonsense. And Kuririn agrees, asking why Goku would be here on Earth if he's an alien.
Raditz says it's simple. Kakarrot was sent here to get rid of all the humans that were in the way. They Saiyans clear planets of its inhabitants and sell it. Adults are sent to planets with high battle power inhabitants, but for a weak planet like this, they send babies, who can get stronger with the help of the planet's moon. Goku asks about the moon, and Raditz explains how looking at the full moon brings out their specialty. Kame-Sen'nin, Bulma, and Kuririn all realize what he means by that, but Goku still has no idea about Ōzaru. Then Raditz freaks out and asks what happened to his tail, and Goku explains it was cut off a while ago. Raditz gets really pissed at these humans, but Goku yells at him that they ain't related, it's like Kuririn said.
Goku tells Raditz to go home, he's Son Goku who was raised here, and everyone else agrees. Raditz then explains that there's only a few Saiyans left in the universe, as Planet Vegeta was destroyed in an explosion caused by a meteor collision. Most of the Saiyans are gone from the universe, including their mother and father. There's only four Saiyans left now, including the two of them. He wants Kakarrot to come with them, it's fun, and it's in his blood.
Goku still refuses, and then Raditz asks him if that's his kid back there. Raditz thinks maybe his son will lend a hand, and Goku tells him he'll knock him out if he comes any closer. But in a split second, Raditz pounds Goku in the stomach, taking him down, and then he grabs Gohan. As Gohan wails, Raditz tells Kakarrot he has one day to reconsider things. He has until this time tomorrow to show him one hundred dead Earthlings. He wants to avoid killing his little brother's kid, if he can.