DB Chapter 147
From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
"The Demon King of Old... Restored!" (若がえるか！？ピッコロ大魔王, Waka Gaeru ka!? Pikkoro Daimaō; Literally meaning "Youth Restored?! Piccolo Daimaō") is chapter 147 of the Dragon Ball manga.
Piccolo continues on about regaining his youth, and Tenshinhan notes that that was his plan. Piccolo stands over the Dragon Balls and calls out Shenlong, and the sky turns black. Tenshinhan realizes what a bad thing Piccolo having his youth restored would be, as the Dragon Balls begin to glow. Shenlong shoots up in his usual blaze of glory, impressing all the onlookers. Tenshinhan telepathically calls Chiaotzu, telling him to make his wish before Piccolo does.
"Now, speak thy wish. Any wish, but only one, and I shall grant it." Piccolo starts to call out his wish, when Chiaotzu runs out. "Please erase..." Piccolo turns his head. "...Piccolo Daimaō..." Piccolo blasts Chiaotzu before he can finish the wish, killing him on the spot. Tenshinhan is pissed, but there's nothing he can do (he can't even speak aloud). Shenlong tells Piccolo to hurry it up, so he yells out his wish to have his youth restored. Shenlong says it's an easy thing, and Piccolo slowly begins to lose all of his wrinkles.
Piccolo gets excited, as he can now feel the incredible power of his restored youth flowing through him. Goku notices the black sky, and realizes that guy has summoned Shenlong. Yajirobe recognizes that name, and that it means all seven balls have been gathered, as Karin Tower comes into view.