DB Chapter 416
From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
"Kamehameha vs. Kamehameha" (かめはめ波対かめはめ波 最後の決戦, Kamehameha Tai Kamehameha Saigo no Kessen; Literally meaning "Kamehameha vs Kamehameha: A Final Showdown") is chapter 416 of the Dragon Ball manga.
The two tremendous Kamehameha head right toward each other. Piccolo says they need to get out of here, and Kuririn takes No. 18, while Tenshinhan and Yamcha take Trunks' body. The two Kamehameha meet halfway, and BOOM! The collision is huge, destroying the surrounding area. The whole world starts shaking, as Gohan and Cell keep going. Piccolo thinks it's no use, and Cell says he'll end this. "Keep it up!!! Keep it up, Gohan!!!! You still haven't let out all of your power!!! Make your power explode!!!!" Gohan insists he already is using his full power. "Somewhere in your heart, you're thinking about how you'll damage the Earth!!! Don't worry about it!!! The damage can be restored with the Dragon Balls!!!"
Cell screams farewell, but suddenly he gets blasted in the face. He looks up, and sees Vegeta. "NOW!!!!" Gohan puts everything into his Kamehameha, and it overwhelms Cell's. Cell is hit, and it completely wipes him out, nucleus and all. Gohan stops, catches his breath, and transforms down from Super Saiyan. He then collapses. There's nothing but a big crater where Cell had been. The others are shocked, while Goku is proud, and Gohan is smiling as he pants.