Board Thread:General Discussion/@comment-10266932-20130531151056/@comment-11051098-20131210175211

Kyūkyoku KON wrote: I could swear I read, saw, (imagined?) that once you've obtained Bankai, you can release your Shikai without saying the release command. I seem to remember this around Renji and Byakuya's fight before Rukia's execution.

I can't remember that being stated, but Renji released Zabimaru's Shikai without saying the release command, in the beginning of that fight, surprising Byakuya. So it might be true.