Pokémon : S3 | E39 – Forest Grumps

Ash and his friends decide to take a break at a nearby lake and relax with their Pokémon out of their Poké Balls. As all the Pokémon are relaxing, they notice something shiny fly through the air. After a few seconds it becomes clear it is a net which opens up and traps all the Pokémon. Team Rocket makes an appearance and announces that they have got the Pokémon and begin to fly away. However, something attacks Team Rocket's balloon with a Hyper Beam. All the Pokémon are freed as a bunch of Ursaring appear. The Ursaring fire Hyper Beam at everybody and begin to charge. Ash and his friends recall their Pokémon and run for their lives with Team Rocket following close behind. They all run into a forest as the Ursaring continue to fire Hyper Beam.

After they escape the Ursaring, everybody realizes that they have all been split up; Ash, Pikachu, and Brock are with Jessie while Misty is with James and Meowth. Jessie decides to have a Pokémon battle with Ash when a bunch of Ursaring show up again. They abandon their battle and run. Meanwhile, Misty challenges James to a battle when Ursaring again show up and they run. A truce is formed between Ash, Brock, and Jessie. Ash then finds out some information on Ursaring using his Pokédex. Misty, James, and Meowth also agree to work together.
(Source: Bulbapedia)