One Piece Chapter 5, page 3-4: CHAPTER 5: THE KING OF THE PIRATES AND THE MASTER SWORDSMAN

Back in the courtyard, Koby is desperately trying to untie Zoro from the execution post. Zoro, exhausted, tells him, "NOW GET OUTTA HERE! THEY'RE ON THEIR WAY DOWN." Koby pants, "BUT... I HAVEN'T UNTIED YOU..." Zoro insists, "DON'T WORRY ABOUT ME. I JUST HAVE TO SURVIVE THE MONTH AND THEY'LL LET ME GO." Koby yells back in frustration, "WHAT ARE YOU SAYING!? THAT IDIOT PROMISED ME! IF I SURVIVE HERE FOR A MONTH, I'LL BE SET FREE!!" Koby reveals the terrible truth: "YOU'RE GOING TO BE EXECUTED THREE DAYS FROM NOW!! THEY'RE NOT GOING TO LET YOU GO! SO JUST BEAT IT--

Koby explains to Zoro that Helmeppo never intended to keep his promise, which is why Luffy punched him. Zoro is stunned, uttering, "WHAT!?" Koby pleads with him, "THE NAVY IS YOUR ENEMY NOW!! PLEASE! IF I UNTIE YOU, WILL YOU HELP LUFFY!?" Zoro remains silent as Koby continues, "HE SAVED MY LIFE! I WON'T ASK YOU TO BECOME A PIRATE, BUT... LUFFY'S REALLY STRONG AND SO ARE YOU! IF YOU TEAM UP......YOU CAN ESCAPE FROM HERE! PLEASE, HELP HIM!