"Preparing for Battle!!" (闘いの準備!!, Tatakai no Junbi!!, Viz: Preparations for Battle) is chapter 17 of the original Naruto manga.
Kakashi, suspicious about how the battle with Zabuza ended, tells Team 7 that Zabuza may still be alive as hunter-nin do not typically take a body elsewhere when destroying it. Since the masked boy did not only this but "killed" Zabuza with senbon, an unusual choice of weapon, the boy was probably saving Zabuza by putting him in a temporary death-like state. In case he is right, Kakashi decides to start training Team 7 to improve their chakra control for another encounter with Zabuza.