Pokémon : S5 | E50 – Entei at Your Own Risk

The group is on their way to Mt. Silver, with Larvitar napping peacefully in Ash's backpack. It wakes up, but Hardens in fear when Misty and Brock talk to it. Ash snuggles Larvitar, promising to protect it from scary Trainers like Misty, which leads to criticisms from Brock that Ash is babying it. Ash's only response is to rub the fact that Larvitar opens up only to him and Pikachu in Misty and Brock's faces, which irritates both of them. Misty tells him that he needs to see how it has improved around other Pokémon. At that moment, a very angry wild Ursaring comes out of the scrub and chases the group away, firing Hyper Beams.

Having lost the Ursaring, the group stops to catch their breath. Larvitar wanders over and discovers a hot spring. Brock notices a variety of wild Pokémon sitting serenely in the hot water. Ash walks forward to test the water but sets off an alarm by breaking a tripwire with his foot. A boy walks out from the growth, calling a challenge to Entei, only to discover the group instead. He explains that he has studied all of the recent Entei sightings and determined that it is next due to appear at the springs. He introduces himself as Nelson. Just then, the Ursaring comes bursting from the scrub, roaring. However, it doesn't pay attention to the group, but instead dives into the springs, emerging with a roar of pleasure. Nelson explains that the springs have relaxation and even healing powers on Pokémon.
(Source: Bulbapedia)