One Piece Chapter 4, page 6: Chapter 4: The Great Captain Morgan

Luffy asks Zoro where his swords are. Zoro explains that Captain Morgan's idiot son took them, noting, "Next to my life, those swords are my dearest treasures." Luffy gets an idea and offers to retrieve them from Helmeppo. However, he adds a condition: "Then, if you want your swords back... you'll have to join my crew!" Zoro angrily calls him a "little rat," but Luffy just laughs and runs off toward the Marine fortress, shouting, "See ya soon!" Zoro watches him go, muttering, "He's going into the fortress... That's one dumb pirate!"