DB Chapter 320
From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
"The End of Namek?" (消え去るナメック星と希望, Kiesaru Namekku-sei to Kibō; Literally meaning "Planet Namek and Hope Disappear") is chapter 320 of the Dragon Ball manga.
The energy ball hits the planet, and boom... Kaiō notices this, and tells the others that Son Goku did well, and he certainly could've won one-on-one, but Freeza decided to destroy Planet Namek, and he'll survive its destruction. But then someone interrupts and says, "Kaiō, can you hear me?! It is I, the God of Earth." Kaiō dismally says he hears him. God says Mister Popo is now gathering all of the Dragon Balls and soon he'll have them all, then they can wish back those at Kaiō's place. But then Kaiō perks up and realizes God's still alive, so Piccolo must be alive also. "Planet Namek isn't gone!!! Goku, Gohan, Piccolo, and the girl are all still alive!!!"
Goku and Freeza are both floating over a giant hole in the planet, with sparks coming out of it. Freeza realizes he didn't use enough power, and Goku says he just escaped death. Freeza laughs and tells him he doesn't know anything. Freeza asks if he knows what happens if the planet's core is destroyed, and explains that in about five minutes, there'll be a much larger explosion that will turn Planet Namek into space dust. Kaiō freaks out, and Goku is a bit surprised too. But then Goku says five minutes is plenty. He can defeat Freeza, take his friends, and escape to Earth on his spaceship in that time. But Freeza says he's the only one with any hope left, much greater than Goku's. He's going to show his full power now. Goku figures he probably never used his full power before because his body couldn't handle it.
Goku yells that he doesn't have time to waste, and he'll settle this now. But Freeza hits Goku with a shockwave, knocking him down into the water. Goku resurfaces, with little damage, although he's now missing half of his shirt. Freeza says this is still only 70% of his full power. Goku flies at Freeza, as he says, "And this will be my long-awaited one hundred percent!!"