7x30 - Dragon Ball Z: Dragon Box

Goku transforms to Super Saiyan 3, but against (pure) Majin Boo, even his power comes up short. Vegeta cannot help himself but fight Boo in Goku's place when Goku goes down, but proves to be no match for Boo's tremendous power. Goku then steps forward to confront Boo again, while providing cover for Vegeta. Unwittingly, Vegeta ends up whispering under his breath, "Kakarrot, you are Number One."