Naruto Episode 40: Kakashi and Orochimaru: Face-to-Face!
Episode 40 of 220 of Naruto, aired July 9, 2003, 25 minutes. Available with English subtitles and dub where released.
Episode summary
While Shino and Zaku finish their fight, Kakashi works on Sasuke's cursed seal. However, someone sinister shows up to ruin things, will Kakashi be able to protect Sasuke from this skilled foe?