The Training Begins…?! (修行開始…!?, Shūgyō Kaishi…!?) is chapter 150 of the Naruto manga.
Naruto and Jiraiya stopped at a fair to gather information on Tsunade. When Naruto said that he wanted to enjoy the fair, Jiraiya took most of his money so that he, a ninja, will not over-indulge himself. After spending what little money he was allowed and buying Jiraiya some food as thanks, Naruto found that Jiraiya had not taken his own advice; not only had he surrounded himself with women and alcohol, but he had spent Naruto's money in order to do so. As Naruto yelled at him he earned the anger of Gantetsu. Jiraiya dealt with Gantetsu, at the same time demonstrating the Rasengan. To start Naruto on his way of learning the Rasengan, Jiraiya instructed him to pop a water balloon by spinning his chakra.
When Naruto falls and drops Jiraiya's things, Jiraiya's savings pass book falls out with the numbers and letters D-1237 on its front cover.