"The Other Side of the Betrayal!!" (裏切りの裏側!!, Uragiri no Uragawa!!) is chapter 304 of the original Naruto manga.
Kabuto arrives to rescue Sai. He undoes his restraints so that they can team up in fighting Team 7, but Sai instead decides to restrain Kabuto. Sai wishes to learn more about bonds by helping Naruto reunite with Sasuke, which Team 7 accepts. They tie Kabuto up and he tells them where to find Sasuke, but adds that they won't accomplish anything. Team 7 splits up and, while searching with Naruto, Sai remembers how he wanted to finish his picture book: he and his brother together. He gives a genuine smile over thoughts of his brother, just as Orochimaru appears and asks about Sai's loyalties.