Farther down the trail, the group discover the Pokémon Center that is on their map, and they enter just as it begins to rain. Despite Brock’s concerns, Ash reassures him and points out that there is no way Charmander would have waited around that long. However, they overhear laughter nearby, and look over to see a Trainer named Damian surrounded by a group of friends. They listen in on his conversation; Damian reveals that he had a Charmander, but since he was so weak, he left him on a rock out in the middle of the woods promising to return for him, though he admits he has no intention of doing so. Ash and his friends conclude that the Charmander they saw, and the Charmander that Damian abandoned, are one and the same. This pushes the normally calm Brock over the edge, and he confronts Damian, demanding he retrieves his Charmander. Damian pushes him off, but Ash and Misty soon arrive to back up Brock. After Damian and his crew leave, Ash and his friends hurry back to find Charmander.
(Source: Bulbapedia)