Didn’t he say it in chapter 402, during Enies Lobby arc? He asked Chopper to get the key to his and Ussop’s cuffs, telling him either Franky, Sanji or Nami could have it. Of course, in the manga, it’s not clear if that line is from him or from Ussop, while I remember clearly that in the anime they had Zoro say the line.